SGS Thomson Microelectronics ST62T45BQ6, ST62P45BQ6, ST62P45BQ1, ST62E45BG1, ST6245BQ6 Datasheet

March 1998 1/72

R

Rev. 2.3

ST62T45B/E45B

8-BIT OTP/EPROM MCU WITH LCD DRIVER,

EEPROM AND A/D CONVERTER

■ 3.0 to 6.0V Supply Operating Range

■ 8 MHz Maximum Clock Frequency

■

-40 to +85°C Operating Temperature Range

■

Run, Wait and Stop Modes

■ 5 Interrupt Vectors

■ Look-up Table capability in Program Memory

■

Data Storage in Program Memory:
User selectable size

■ Data RAM: 128 bytes

■ Data EEPROM: 128 bytes

■

User Programmable Options

■ 19 I/O pins, fully programmable as:

– Input with pull-up resistor
– Input without pull-up resistor
– Input with interrupt generation
– Open-drain or push-pull output
– Analog Input
– LCD segments (8 combiport lines)

■

4 I/O lines can sink up to 20mA to drive LEDs or
TRIACs directly

■ Two 8-bit Timer/Counter with 7-bit

programmable prescaler

■

Digital Watchdog

■

8-bit A/D Converter with 7 analog inputs

■ 8-bit Synchronous Peripheral Interface (SPI)

■ LCD driver with 24 segment outputs, 4

backplane outputs and selectable multiplexing
ratio.

■ 32kHz oscillator for stand-by LCD operation

■ On-chip Clock oscillatorcan be driven byQuartz

Crystal or Ceramic resonator

■ One external Non-Maskable Interrupt

■ ST6245-EMU2 Emulation and Development

System (connects to an MS-DOS PC via a
parallel port).

DEVICE SUMMARY

(See end of Datasheet for Ordering Information)

PQFP52

CQFP52W

DEVICE

OTP

(Bytes)

EPROM

(Bytes)

I/O Pins

ST62T45B 3884 - 11 to 19
ST62E45B 3884 11 to 19

1

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Table of Contents

72

2

ST62T45B/E45B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1 GENERAL DESCRIPTION . . . . . . . ...............................................5

1.1 INTRODUCTION .........................................................5

1.2 PIN DESCRIPTIONS . . . . . . . . . . ............................................7

1.3 MEMORYMAP ..........................................................8

1.3.1 Introduction . . . . . . . . ................................................8

1.3.2 Program Space . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........................9

1.3.3 Data Space . . . . . . . . ...............................................10

1.3.4 Stack Space . . . . . . . . . . . . . . . . . ......................................10

1.3.5 Data Window Register (DWR) . . . . . . . . . . . . . . . . . . . . .....................11

1.3.6 Data RAM/EEPROM Bank Register (DRBR)..............................12

1.3.7 EEPROM Description ...............................................13

1.4 PROGRAMMING MODES .................................................15

1.4.1 Option Byte . . . . . . . . ...............................................15

1.4.2 Program Memory . . . . ...............................................15

1.4.3 EEPROM Data Memory . . . . . . . . . . . . ..................................15

1.4.4 EPROMErasing....................................................15

2 CENTRAL PROCESSING UNIT .................................................16

2.1 INTRODUCTION ........................................................16

2.2 CPU REGISTERS . . . . . . . . ...............................................16

3 CLOCKS, RESET, INTERRUPTS AND POWER SAVING MODES . . . . . . . ..............18

3.1 CLOCKSYSTEM........................................................18

3.1.1 Main Oscillator . . . . . . . . . . ...........................................18

3.1.2 32kHz STAND-BY OSCILLATOR ......................................19

3.2 RESETS...............................................................20

3.2.1 RESET Input ......................................................20

3.2.2 Power-on Reset . . . . . . . . . . . . . . . .....................................20

3.2.3 Watchdog Reset . . . . ...............................................21

3.2.4 Application Notes . . . . ...............................................21

3.2.5 MCU Initialization Sequence ..........................................21

3.3 DIGITAL WATCHDOG . . . . . . . . . . . . . . . .....................................23

3.3.1 Digital Watchdog Register (DWDR) . . . ..................................25

3.3.2 Application Notes . . . . ...............................................25

3.4 INTERRUPTS . . . . ......................................................27

3.4.1 Interrupt request . . . . . . . . . . . . . . . .....................................27

3.4.2 Interrupt Procedure . . . ..............................................28

3.4.3 Interrupt Option Register (IOR) . . . . ....................................29

3.4.4 Interrupt Sources . . . . ...............................................29

3.5 POWER SAVING MODES .................................................31

3.5.1 WAIT Mode . . . . . . . . ...............................................31

3.5.2 STOPMode.......................................................31

3.5.3 Exit from WAIT and STOP Modes . . . ...................................32

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Table of Contents

3

4 ON-CHIP PERIPHERALS . . . ...................................................33

4.1 I/OPORTS.............................................................33

4.1.1 Operating Modes . . . . ...............................................34

4.1.2 Safe I/O State Switching Sequence. . . ..................................35

4.1.3 LCD alternate functions (combiports) ...................................37

4.1.4 SPI alternate functions . . . ............................................37

4.1.5 I/O Port Option Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................38

4.1.6 I/O Port Data Direction Registers . . . ....................................38

4.1.7 I/O Port Data Registers . . . . ..........................................38

4.2 TIMER1&2............................................................39

4.2.1 TIMER 1 Operating Modes . . . . . . .....................................41

4.2.2 TIMER 2 Operating Mode . . . . . . . . . . . . . . . . . . . . ........................41

4.2.3 Timer Interrupt . . . . . . . . . . ...........................................41

4.2.4 Application Notes . . . . ...............................................41

4.2.5 TIMER 1 Registers . .................................................42

4.2.6 TIMER 2 Registers . .................................................43

4.3 A/D CONVERTER (ADC) . . . ..............................................44

4.3.1 Application Notes . . . . ...............................................44

4.4 SERIAL PERIPHERAL INTERFACE (SPI) . . . . . . . . . . . . ........................46

4.5 LCD CONTROLLER-DRIVER . . . . ..........................................48

4.5.1 Multiplexing ratio and frame frequency setting . . . . ........................49

4.5.2 Segment and common plates driving. . ..................................49

4.5.3 LCDRAM.........................................................50

4.5.4 Stand by or STOP operation mode . . . . . . . . . . ...........................51

4.5.5 LCD Mode Control Register (LCDCR)...................................51

5SOFTWARE ................................................................52

5.1 ST6 ARCHITECTURE . . . . . . . . . . . . . . . .....................................52

5.2 ADDRESSING MODES . . . . ...............................................52

5.3 INSTRUCTION SET . . . ...................................................53

6 ELECTRICAL CHARACTERISTICS. . . . . . . . . . . . ..................................58

6.1 ABSOLUTE MAXIMUM RATINGS. ..........................................58

6.2 RECOMMENDED OPERATING CONDITIONS. . . ..............................59

6.3 DC ELECTRICAL CHARACTERISTICS ......................................60

6.4 AC ELECTRICAL CHARACTERISTICS ......................................61

6.5 A/D CONVERTER CHARACTERISTICS. . . ...................................61

6.6 TIMER CHARACTERISTICS . . . ............................................62

6.7 SPI CHARACTERISTICS . . . ..............................................62

6.8 LCD ELECTRICAL CHARACTERISTICS . . . . . . . . . . ...........................62

6.9 PSS ELECTRICAL CHARACTERISTICS (WHEN AVAILABLE). . . . . . . . . . . . . . . .....62

7 GENERAL INFORMATION . . . . . . . . . . ...........................................63

7.1 PACKAGE MECHANICAL DATA. . . . ........................................63

7.2 PACKAGE THERMAL CHARACTERISTIC . . ..................................64

7.3 ORDERING INFORMATION ...............................................64

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Table of Contents

72

1

ST62P45B . ........................................65

1 GENERAL DESCRIPTION . . . . . . . ..............................................66

1.1 INTRODUCTION ........................................................66

1.2 ORDERING INFORMATION ...............................................66

1.2.1 Transfer of Customer Code . ..........................................66

1.2.2 Listing Generation and Verification . . . . . . . . . . ...........................66

ST6245B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

1 GENERAL DESCRIPTION . . . . . . . ..............................................70

1.1 INTRODUCTION ........................................................70

1.2 ROM READOUT PROTECTION . . . . . . . . . . . . . . . . . . . . ........................70

1.3 ORDERING INFORMATION ...............................................72

1.3.1 Transfer of Customer Code . ..........................................72

1.3.2 Listing Generation and Verification . . . . . . . . . . ...........................72

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ST62T45B/E45B

1 GENERAL DESCRIPTION

1.1 INTRODUCTION

The ST62T45B and ST62E45B devices are low
cost members of the ST62xx 8-bit HCMOS family
of microcontrollers, which are targeted at low to
medium complexity applications. All ST62xx de­vices are based on a building block approach: a

common core is surrounded by a number of on­chip peripherals.

The ST62E45B is the erasable EPROM version of
the ST62T45B device, which may be used to em­ulate the ST62T45B device, as well as the respec­tive ST6245B ROM devices.

Figure 1. Block Diagram

TEST

NMI INTERRUPT

PROGRAM

PC

STACK LEVEL 1
STACK LEVEL 2
STACK LEVEL 3
STACK LEVEL 4
STACK LEVEL 5
STACK LEVEL 6

POWER
SUPPLY

OSCILLATOR

RESET

DATA ROM

USER

SELECTABLE

DATA RAM

PORT A

PORT B

TIMER 1

DIGITAL

8 BIT CORE

TEST/V

PP

8-BIT

A/D CONVERTER

PA5..PA7/Ain

V

DDVSS

OSCin OSCout RESET

WATCHDOG

Memory

PORT C

SPI (SERIAL

PERIPHERAL

INTERFACE)

128 Bytes

3884 bytes

DATA EEPROM

128 Bytes

PB0..PB3/Ain

PC0..PC7/S33..S40

S17..S32
COM1..COM4

(VPP on EPROM/OTP versions only)

PB4/20mA Sink
PB5/Scl/20mA Sink
PB6/Sin/20mA Sink
PB7/Sout/20mA Sink

VLCD
VLCD1/3
VLCD2/3

OSC 32kHz

TIMER 2

OSC32in
OSC32out

LCD DRIVER

VR01994

TIMER

4

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ST62T45B/E45B

INTRODUCTION (Cont’d)

OTP and EPROM devices are functionally identi­cal. The ROM based versions offer the same func­tionality selecting as ROM options the options de­fined in the programmable option byte of the
OTP/EPROM versions.OTP devices offer all the
advantages of user programmability at low cost,
which make them the ideal choice in a wide range
of applications where frequent code changes,
multiple code versions or last minute programma­bility are required.

These compact low-cost devices feature two Tim­ers comprising an 8-bit counter and a 7-bit pro­grammable prescaler, EEPROM data capability, a
serial synchronous port interface (SPI), an 8-bit
A/D Converter with 8 analog inputs, a Digital
Watchdog timer, and a complete LCD controller
driver, making them well suited for a wide range of
automotive, appliance and industrial applications.

Figure 2. 52 Pin QFP Package

Table 1. ST6245B Pin Description

*Note: 20mA Sink

27

14

13

40

52

12

3

39

26

VR01649C

Pin

number

Pin

name

Pin

number

Pin

name

Pin

number

Pin

name

Pin

number

Pin

name

1 COM4 14 RESET 27 OSC32out 40 S28
2 COM3 15 OSCout 28 OSC32in 41 S29
3 COM2 16 OSCin 29 S17 42 S30
4 COM1 17 NMI 30 S18 43 S31
5 VLCD1/ 3 18 TIMER 31 S19 44 S32
6 VLCD2/ 3 19 PB7/ Sout * 32 S20 45 PC0/S33
7 VLCD 20 PB6/ Sin* 33 S21 46 PC1/S34
8 PA7/Ain 21 PB5/ SCL * 34 S22 47 PC2/S35

9 PA6/Ain 22 PB4 * 35 S23 48 PC3/S36
10 PA5/ Ain 23 PB3/ Ain 36 S24 49 PC4/S37
11 TEST 24 PB2/ Ain 37 S25 50 PC5/S38
12 VDD 25 PB1/Ain 38 S26 51 PC6/S39
13 VSS 26 PB0/Ain 39 S27 52 PC7/S40

5

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ST62T45B/E45B

1.2 PIN DESCRIPTIONS
VDDand V

SS

. Power is supplied to the MCU via
these two pins. VDDis the power connection and
VSSis the ground connection.

OSCin and OSCout. These pins are internally
connected to the on-chip oscillator circuit. Aquartz
crystal, a ceramic resonator or an external clock
signal can be connected between these two pins.
The OSCin pin is the input pin, the OSCout pin is
the output pin.

RESET

. The active-low RESET pin is used to re-

start the microcontroller.
TEST/VPP. The TEST must be held at VSSfor nor-

mal operation (an internal pull-down resistor se­lects normal operating mode if TEST pin is not
connected). If TEST pin is connected to a +12.5V
level during the reset phase, the EPROM/OTP
programming Mode is entered.

NMI.

The NMI pin provides the capability for asyn­chronous interruption, by applying an external non
maskable interrupt to the MCU.The NMI input is
falling edge sensitive with Schmitt trigger charac­teristics. The user can select as option the availa­bility of an on-chip pull-up at this pin.

PA5-PA7. These 3 lines are organised as one I/O
port (A). Each line may be configured under soft­ware control as input with or without internal pull­up resistors, input with interrupt generation and
pull-up resistor, open-drain or push-pull output, or
as analog input for the A/D converter.

PB0...PB7. These 8 lines are organised as one
I/O port (B). Each line may be configured under
software control as input with or without internal
pull-up resistors, input with interrupt generation
and pull-up resistor, open-drain or push-pull
output, analog input for the A/D converter.
PB0..PB3 can be used as analog inputs for the
A/D converter , while PB7/Sout, PB6/Sin and
PB5/Scl can be used respectively as data out,
data in and Clock pins for the on-chip SPI. In addi-

tion, PB4..PB7 can sink 20mA for direct LED or
TRIAC drive.

PC0-PC7. These 8 lines are organised as one I/O
port (C). Each line may be configured under soft­ware control as input with or without internal pull­up resistor, input with interrupt generation and
pull-up resistor, open-drain or push-pull output, or
as LCD segment output S33..S40.

COM1-COM4

. These four pins are the LCD pe­ripheral common outputs. They are the outputs of
the on-chip backplane voltage generator which is
used for multiplexing the 45 LCD lines allowing up
to 180 segments to be driven.

S17..S40. These pins are the 24 LCD peripheral
segment outputs. S33..S40 are alternate functions
of the Port C I/O pins. (Combiports feature)

VLCD

. Display voltage supply. It determines the
high voltage level on COM1-COM4 and S4-S48
pins.

VLCD1/3, VLCD2/3

. Display supply voltage inputs
for determining the display voltage levels on
COM1-COM4 and S4-S48 pins during multiplex
operation.

OSC32in

and

OSC32out

. These pins are inter­nally connected with the on-chip 32kHz oscillator
circuit. A 32.768kHz quartz crystal can be con­nected between these two pins if it is necessary to
provide the LCD stand-by clock and real time in­terrupt. OSC32in is the input pin, OSC32out is the
output pin.

TIMER. This is the TIMER 1 I/O pin. In input
mode, it is connected to the prescaler and acts as
external timer clock or as control gate for the in­ternal timer clock. In output mode, the TIMER pin
outputs the data bit when a time-out occurs.The
user can select as option the availability of an on­chip pull-up at this pin.

6

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ST62T45B/E45B

1.3 MEMORY MAP

1.3.1 Introduction

The MCU operates in three separate memory
spaces: Program space, Data space, and Stack
space. Operation in these three memory spaces is
described in the following paragraphs.

Briefly, Program space contains user program
code in Program memory and user vectors; Data
space contains user data in RAM and in Program
memory, and Stack space accommodates six lev­els of stack for subroutine and interrupt service
routine nesting.

Figure 3. Memory Addressing Diagram

PROGRAM SPACE

PROGRAM

INTERRUPT &

RESET VECTORS

ACCUMULATOR

DATA RAM

BANK SELECT

WINDOW SELECT

RAM

X REGISTER
Y REGISTER
V REGISTER

W REGISTER

DATA READ-ONLY

WINDOW

RAM / EEPROM
BANKING AREA

000h

03Fh
040h

07Fh
080h
081h
082h
083h
084h

0C0h

0FFh

0-63

DATA SPACE

0000h

0FF0h

0FFFh

MEMORY

MEMORY

DATA READ-ONLY

MEMORY

VR01568

7

9/72

ST62T45B/E45B

MEMORY MAP (Cont’d)

1.3.2 Program Space

Program Space comprises the instructions to be
executed, the data required for immediate ad­dressing mode instructions, the reserved factory
test area and the user vectors. Program Space is
addressed via the 12-bit Program Counter register
(PC register).

1.3.2.1 Program Memory Protection

The Program Memory in OTP or EPROM devices
can be protected against external readout of
memory by selecting the READOUT PROTEC­TION option in the option byte.

In the EPROM parts, READOUT PROTECTION
option can be disactivated only by U.V. erasure
that also results into the whole EPROM context
erasure.

Note:

Once the Readout Protection is activated, it
is no longer possible, even for SGS-THOMSON,
to gain access to the Program memory contents.
Returned parts with a protection set can therefore
not be accepted.

Figure 4. ST62E45B/T45B Program

Memory Map

0000h

RESERVED

*

USER

PROGRAM MEMORY

(OTP/EPROM)

3872 BYTES

0F9Fh

0FA0h
0FEFh
0FF0h
0FF7h
0FF8h
0FFBh

0FFCh
0FFDh

0FFEh
0FFFh

RESERVED

*

RESERVED

INTERRUPT VECTORS

NMI VECTOR

USER RESET VECTOR

0080h

(*) Reserved areas should be filled with 0FFh

007Fh

8

10/72

ST62T45B/E45B

MEMORY MAP (Cont’d)

1.3.3 Data Space

Data Space accommodates all the data necessary
for processing the user program. This space com­prises the RAM resource, the processor core and
peripheral registers, as well as read-only data
such as constants and look-up tables in Program
memory.

1.3.3.1 Data ROM

All read-only data is physically stored in program
memory, which also accommodates the Program
Space. The program memory consequently con­tains the program code to be executed, as well as
the constants and look-up tables required by the
application.

The Data Space locations in which the different
constants and look-up tables are addressed by
the processor core may be thought of as a 64-byte
window through which it is possible to access the
read-only data stored in Program memory.

1.3.3.2 Data RAM/EEPROM

In ST62T45B and ST62E45B devices, the data
space includes 60 bytes of RAM, the accumulator
(A), the indirect registers (X), (Y), the short direct
registers (V), (W), the I/O port registers, the pe­ripheral data and control registers, the interrupt
option register and the Data ROM Window regis­ter (DRW register).

Additional RAM and EEPROM pages can also be
addressed using banks of 64 bytes located be­tween addresses 00h and 3Fh.

1.3.4 Stack Space

Stack space consists of six 12-bit registers which
are used to stack subroutine and interrupt return
addresses, as wellas the current program counter
contents.

Table 2. Additional RAM/EEPROM Banks.

Table 3. ST62T45B/E45B Data Memory Space

Device RAM EEPROM

ST62T45B/E45B 1 x 64 bytes 2 x 64 bytes

DATAand EEPROM

000h
03Fh

DATA ROM WINDOW AREA

040h

07Fh
X REGISTER 080h
Y REGISTER 081h
V REGISTER 082h

W REGISTER 083h

DATARAM

084h

0BFh
PORT A DATAREGISTER 0C0h
PORT B DATAREGISTER 0C1h

SPI INTERRUPT DISABLE REGISTER 0C2h

PORT C DATAREGISTER 0C3h

PORT A DIRECTION REGISTER 0C4h
PORT B DIRECTION REGISTER 0C5h
PORT C DIRECTION REGISTER 0C6h

RESERVED 0C7h
INTERRUPT OPTION REGISTER 0C8h*
DATA ROM WINDOW REGISTER 0C9h*

RESERVED 0CAh*

RAM/EEPROM BANK SELECT REGISTER 0CBh*

PORT A OPTION REGISTER 0CCh

RESERVED 0CDh

PORT B OPTION REGISTER 0CEh
PORT C OPTION REGISTER 0CFh

A/D DATAREGISTER 0D0h

A/D CONTROL REGISTER 0D1h

TIMER 1 PRESCALER REGISTER 0D2h

TIMER 1 COUNTER REGISTER 0D3h

TIMER 1 STATUS/CONTROLREGISTER 0D4h

TIMER 2 PRESCALER REGISTER 0D5h

TIMER 2 COUNTER REGISTER 0D6h

TIMER 2 STATUS/CONTROLREGISTER 0D7h

WATCHDOGREGISTER 0D8h

RESERVED 0D9h

RESERVED 0DAh

32kHz OSCILLATOR CONTROL REGISTE R 0DBh

LCD MODE CONTROL REGISTER 0DCh

SPI DATAREGISTER 0DDh

RESERVED 0DEh

EEPROM CONTROL REGISTER 0DFh

LCD RAM

0E0h
0F7h

DATA RAM

0F8h
0FEh

ACCUMULATOR OFFh

* WRITE ONLYREGISTER

9

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ST62T45B/E45B

MEMORY MAP (Cont’d)

1.3.5 Data Window Register (DWR)

The Data Read-Only Memory window is located
from address 0040h to address 007Fh in Data
space. It allows direct reading of 64 consecutive
bytes located anywhere in program memory, be­tween address 0000h and 1FFFh (top memory ad­dress depends on the specific device). All the pro­gram memory can therefore beused to store either
instructions or read-only data. Indeed, the window
can be moved in steps of 64 bytes along the pro­grammemory by writingthe appropriate codein the
Data Window Register (DWR).

The DWR can be addressed like any RAM loca­tion in the Data Space, it is however a write-only
register and therefore cannot be accessed using
single-bit operations. This register is used to posi­tion the 64-byte read-only data window (from ad­dress 40h to address 7Fh of the Data space) in
program memory in 64-byte steps. The effective
address of the byte to be read as data in program
memory is obtained by concatenating the 6 least
significant bits of the register address given in the
instruction (as least significant bits) and the con­tent of the DWR register (as most significant bits),
as illustrated in Figure 5 below. For instance,
when addressing location 0040h of the Data
Space, with 0 loaded in the DWR register, the
physical location addressed in program memory is
00h. The DWR register is not cleared on reset,
therefore it must be written to prior to the first ac­cess to the Data read-only memory window area.

Data Window Register (DWR)

Address: 0C9h — Write Only

Bits 7, 6 = Not used.
Bit 5-0 =

DWR5-DWR0:

Data read-only memory

Window Register Bits.

These are the Data read­only memory Window bits that correspond to the
upper bits of the data read-only memory space.

Caution:

This register is undefined on reset. Nei­ther read nor single bit instructions may be used to
address this register.

Note:

Care is required when handling the DWR
register as it is write only. For this reason, the
DWR contents should not be changed while exe­cuting an interrupt service routine, as the service
routine cannot save and then restore the register’s
previous contents. If it is impossible to avoid writ­ing to the DWR during the interrupt service rou­tine, an image of the register must be saved in a
RAM location, and each time the program writes
to the DWR, it must also write to the image regis­ter. The image register must be written first so
that, if an interrupt occurs between the two instruc­tions, the DWR is not affected.

Figure 5. Data read-only memory Window Memory Addressing

70

- - DWR5 DWR4 DWR3 DWR2 DWR1 DWR0

DATA ROM

WINDOW REGISTER

CONTENTS

DATA SPACEADDRESS

40h-7Fh

IN INSTRUCTION

PROGRAMSPACE ADDRESS

765432 0

543210

543210

READ

1

67891011

0

1

VR01573C

12

1

0

DATA SPACEADDRESS

:

:

59h

000

0

1

00

1

11

Example:

(DWR)

DWR=28h

11

0000000

1

ROM

ADDRESS:A19h

11

13

0

1

10

12/72

ST62T45B/E45B

MEMORY MAP (Cont’d)

1.3.6 Data RAM/EEPROM Bank Register
(DRBR)

Address: CBh — Write only

Bit 7-5 = These bits are not used
Bit 4 - DRBR4. This bit, when set, selects RAM

Page 2.
Bit 3 - DRBR3. This bit, when set, selects RAM

Page 1.
Bit2. These bits are not used.
Bit 1 - DRBR1. This bit, when set, selects

EEPROM Page 1.
Bit 0 - DRBR0. This bit, when set, selects

EEPROM Page 0.
The selection of the bank is made by program-

ming the Data RAM Bank Switch register (DRBR
register) located at address CBh of the Data
Space according to Table 1. No more than one
bank should be set at a time.

The DRBR register can be addressed like a RAM
Data Space at the address CBh; nevertheless it is
a write only register that cannot be accessed with
single-bit operations. This register is used to se­lect the desired 64-byte RAM/EEPROM bank of
the Data Space. The number of banks has to be
loaded in the DRBR register and the instruction
has to point to the selected location as if it was in
bank 0 (from 00h address to 3Fh address).

This register is not cleared during the MCU initial­ization, therefore it must be written before the first
access to the Data Space bank region. Refer to
the Data Space description for additional informa­tion. The DRBR register is not modified when an
interrupt or a subroutine occurs.

Notes :
Care is required when handling the DRBR register

as it is write only. For this reason, it is not allowed
to change the DRBR contents while executing in­terrupt service routine, as the service routine can­not save and then restore its previous content. If it
is impossible to avoid the writing of this register in
interrupt service routine, an image of this register
must be saved in a RAM location, and each time
the program writes to DRBR it must write also to
the image register. The image register must be
written first, so if an interrupt occurs between the
two instructions the DRBR is not affected.

In DRBR Register, only 1 bit must be set. Other­wise two or more pages are enabled in parallel,
producing errors.

Table 4. Data RAM Bank Register Set-up

70

- - - DRBR4 DRBR3 - DRBR1 DRBR0

DRBR ST62T45B/E45B

00h None
01h EEPROM Page 0
02h EEPROM Page 1
08h Not available
10h RAM Page 2

other Reserved

11

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ST62T45B/E45B

MEMORY MAP (Cont’d)

1.3.7 EEPROM Description

EEPROM memory is located in 64-byte pages in
data space. This memory may be used by the user
program for non-volatile data storage.

Data space from 00h to 3Fh is paged as described
in Table 5. EEPROM locations are accessed di­rectly by addressing these paged sections of data
space.

The EEPROM does not require dedicated instruc­tions forread or writeaccess. Once selected viathe
Data RAM Bank Register, the active EEPROM
page is controlled by the EEPROM Control Regis­ter (EECTL), which is described below.

BitE20FF oftheEECTL register mustbe reset prior
to any write or read access to the EEPROM. If no
bank has been selected, or if E2OFF is set, any ac­cess is meaningless.

Programming must be enabled by setting the
E2ENA bit of the EECTL register.

The E2BUSY bit of the EECTL register isset when
the EEPROM is performing a programming cycle.
Any access to the EEPROM when E2BUSY is set
is meaningless.

Provided E2OFF and E2BUSY are reset, an EEP­ROM location is read just like any other data loca­tion, also in terms of access time.

Writing to the EEPROM may be carried out in two
modes: Byte Mode (BMODE) and Parallel Mode

(PMODE). In BMODE, one byte is accessed at a
time, while in PMODE up to 8 bytes in the same
row are programmed simultaneously (with conse­quent speed and power consumption advantages,
the latter being particularly important in battery
powered circuits).

General Notes:
Data should be written directly to the intended ad-

dress in EEPROM space. There is no buffer mem­ory between data RAM and the EEPROM space.

When the EEPROM is busy (E2BUSY = “1”)
EECTL cannot be accessed in write mode, it is
only possible to read the status of E2BUSY. This
implies that as long as the EEPROM is busy, it is
not possible to change the status of the EEPROM
Control Register. EECTL bits 4 and 5 are reserved
and must never be set.

Care is required when dealing withthe EECTL reg­ister, as some bits are write only. For this reason,
the EECTL contents must not be altered while ex­ecuting an interrupt service routine.

If it is impossible to avoid writing to this register
within an interrupt service routine, an image of the
register must be saved in a RAM location, and
each time the program writes to EECTL it must
also write to the image register. The image regis­ter must be written to first so that, ifan interrupt oc­curs between the two instructions, the EECTL will
not be affected.

Table 5. Row Arrangement for Parallel Writing of EEPROM Locations

Dataspace
addresses.
Banks 0 and 1.

Byte 01234567
ROW7 38h-3Fh
ROW6 30h-37h
ROW5 28h-2Fh
ROW4 20h-27h
ROW3 18h-1Fh
ROW2 10h-17h
ROW1 08h-0Fh
ROW0 00h-07h

Up to 8 bytes in each row may be programmed simultaneously in Parallel Write mode.

The number of available 64-byte banks (1 or 2) is device dependent.

12

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ST62T45B/E45B

MEMORY MAP (Cont’d)
Additional Notes on Parallel Mode:

If the user wishes to perform parallel program­ming, the first step should be to set the E2PAR2
bit. From this time on, the EEPROM will be ad­dressed in write mode, the ROW address will be
latched and it will be possible to change it only at
the end of the programming cycle, or by resetting
E2PAR2 without programming the EEPROM. Af­ter the ROW address is latched, the MCU can only
“see” the selected EEPROM row and any attempt
to write or read other rows will produce errors.

The EEPROM should not be read while E2PAR2
is set.

As soon as the E2PAR2 bit is set, the 8 volatile
ROW latches are cleared. From this moment on,
the user can load data in all or in part of the ROW.
Setting E2PAR1 will modify the EEPROM regis­ters corresponding to the ROW latches accessed
after E2PAR2. For example, if the software sets
E2PAR2 and accesses the EEPROM by writing to
addresses 18h, 1Ah and 1Bh, and then sets
E2PAR1, these three registers will be modified si­multaneously; the remaining bytes in the row will
be unaffected.

Note that E2PAR2 is internally reset at the end of
the programming cycle. This implies that the user
must set the E2PAR2 bit between two parallel pro­gramming cycles. Note that if the user tries to set
E2PAR1 while E2PAR2 is not set, there will be no
programming cycle and the E2PAR1 bit will be un­affected. Consequently, the E2PAR1 bit cannot be
set if E2ENA is low. The E2PAR1 bit can be set by
the user, only if the E2ENA and E2PAR2 bits are
also set.

EEPROM Control Register (EECTL)

Address: DFh — Read/Write
Reset status: 00h

Bit 7 = D7:

Unused.

Bit6=E2OFF:

Stand-by Enable Bit.

WRITE ONLY.
Ifthis bitisset theEEPROM isdisabled (any access
will be meaningless) and thepower consumption of
the EEPROM is reduced to its lowest value.

Bit 5-4 =

D5-D4

:

Reserved.

MUST be kept reset.

Bit 3 =

E2PAR1

:

Parallel Start Bit.

WRITE ONLY.
Oncein ParallelMode,assoon astheusersoftware
sets the E2PAR1 bit, parallel writing of the 8 adja­cent registers will start. This bit is internally reset at
the end of the programming procedure. Note that
less than 8 bytes can be written if required, the un­defined bytes being unaffected by the parallel pro­gramming cycle; this is explained in greater detail
in the Additional Notes on Parallel Mode overleaf.

Bit 2 = E2PAR2:

Parallel Mode En. Bit.

WRITE
ONLY. This bit must be set by the user program in
order to perform parallel programming. If E2PAR2
is set and the parallel start bit (E2PAR1) is reset,
up to 8 adjacent bytes can be written simultane­ously. These 8 adjacent bytes are considered as a
row, whose address lines A7, A6, A5, A4, A3 are
fixed while A2, A1 and A0 are the changing bits,
as illustrated inFigure 5. E2PAR2 is automatically
reset at the end of any parallel programming pro­cedure. It can be reset by the user software before
starting the programming procedure, thus leaving
the EEPROM registers unchanged.

Bit 1 =

E2BUSY

:

EEPROM Busy Bit.

READ ON­LY. This bit is automatically set by the EEPROM
control logic when the EEPROM is in program­ming mode. The user program should test it be­fore any EEPROM read or write operation; any at­tempt to access the EEPROM while the busy bit is
set will be aborted and the writing procedure in
progress will be completed.

Bit 0 =E2ENA:

EEPROM Enable Bit.

WRITE ON­LY. Thisbit enables programming of the EEPROM
cells. It must be set before any write to the EEP­ROM register. Any attempt to write to the EEP­ROM when E2ENA is low is meaningless and will
not trigger a write cycle.

Caution:

This register is undefined on reset. Nei­ther read nor single bit instructions may be used to
address this register.

70

D7 E2OFF D5 D4 E2PAR1 E2PAR2 E2BUSY E2ENA

13

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ST62T45B/E45B

1.4 PROGRAMMING MODES

1.4.1 Option Byte

The Option Byte allows configuration capability to
the MCUs. Option byte’s content is automatically
read, and the selected options enabled, when the
chip reset is activated.

It can only be accessed during the programming
mode. This access is made either automatically
(copy from a master device) or by selecting the
OPTION BYTE PROGRAMMING mode of the
programmer.

The option byte is located in a non-user map. No
address has to be specified.

EPROM Code Option Byte

Bit 7. Reserved.
Bit 6 =

NMI PULL..

This bit must be set high to re­move the NMI pin pull up resistor when it is low, a
pull up is provided.

Bit 5 =

PROTECT

. This bit allows the protection of
the software contents against piracy. When the bit
PROTECT is set high, readout of the OTP con­tents is prevented by hardware. No programming
equipment is able to gain access to the user pro­gram. When this bit is low, the user program can
be read.

Bit 4. Reserved.
Bit 3 =

WDACT

. This bit controls the watchdog ac­tivation. When it is high, hardware activation is se­lected. The software activation is selected when
WDACT is low.

Bit 2 =

TIM PULL.

This bit must be set high to con­figure the TIM pin with a pull up resistor when it is
low, no pull up is provided.

Bit 1-0 = Reserved.

The Option byte is written during programming ei­ther by using the PC menu (PC driven Mode) or
automatically (stand-alone mode)

1.4.2 Program Memory

EPROM/OTP programming mode is set by a
+12.5V voltage applied to the TEST/VPPpin. The
programming flow of the ST62T45B/E45B is de­scribed in the User Manual of the EPROM Pro­gramming Board.

The MCUs can be programmed with the
ST62E4xB EPROM programming tools available
from SGS-THOMSON.

1.4.3 EEPROM Data Memory

EEPROM data pages are supplied in the virgin
state FFh. Partial or total programming of EEP­ROM data memory can be performed either
through the application software, or through an ex­ternal programmer. Any SGS-THOMSON tool
used for the program memory (OTP/EPROM) can
also be used to program the EEPROM data mem­ory.

1.4.4 EPROM Erasing

The EPROM of the windowed package of the
MCUs may be erased by exposure to Ultra Violet
light. The erasure characteristic of the MCUs is
such that erasure begins when the memory is ex­posed to light with a wave lengths shorter than ap­proximately 4000Å. It should be noted that sun­lights and some types of fluorescent lamps have
wavelengths in the range 3000-4000Å.

It is thus recommended that the window of the
MCUs packages be covered by an opaque label to
prevent unintentional erasure problems when test­ing the application in such an environment.

The recommended erasure procedure of the
MCUs EPROM is the exposure to short wave ul­traviolet light which have a wave-length 2537A.
The integrated dose (i.e. U.V. intensity x exposure
time) for erasure should be a minimum of 15W­sec/cm2. The erasure time with this dosage is ap­proximately 15 to 20 minutes using an ultraviolet
lamp with 12000µW/cm2power rating. The
ST62E45B should be placed within 2.5cm (1Inch)
of the lamp tubes during erasure.

70

-

NMI

PULL

PRO­TECT

- WDACT

TIM

PULL

--

14

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ST62T45B/E45B

2 CENTRAL PROCESSING UNIT

2.1 INTRODUCTION

The CPU Core of ST6 devices is independent of
the I/O or Memory configuration. Assuch,it may be
thought of as an independent central processor
communicating with on-chip I/O, Memory and Pe­ripherals via internal address, data, and control
buses. In-core communication is arranged as
shown in Figure 6; the controller being externally
linked to both the Reset and Oscillator circuits,
while the core is linked to the dedicated on-chip pe­ripherals via the serial data bus and indirectly, for
interrupt purposes, through the control registers.

2.2 CPU REGISTERS

TheST6FamilyCPUcore features sixregistersand
three pairs of flags available to the programmer.
These are described in the following paragraphs.

Accumulator (A). The accumulator is an 8-bit
general purpose register used in all arithmetic cal­culations, logical operations, and data manipula­tions. The accumulator can be addressed in Data
space as a RAM location at address FFh. Thus
the ST6 can manipulate the accumulator just like
any other register in Data space.

Indirect Registers (X, Y).These two indirect reg­isters are used as pointers to memory locations in
Data space. They are used in the register-indirect
addressing mode. These registers can be ad­dressed in the data space as RAM locations at ad­dresses 80h (X) and 81h (Y). They can also be ac­cessed with the direct, short direct, or bit direct ad­dressing modes. Accordingly, the ST6 instruction
set can use the indirect registers as any other reg­ister of the data space.

Short Direct Registers (V, W).These two regis­ters are used to save a byte in short direct ad­dressing mode. They can be addressed in Data
space as RAM locations at addresses 82h (V) and
83h (W). They can also be accessed using the di­rect and bit direct addressing modes. Thus, the
ST6 instruction set can use the short direct regis­ters as any other register of the data space.

Program Counter (PC). The program counter is a
12-bit register which contains the address of the
next ROM location to be processed by the core.
This ROM location may be an opcode, an oper­and, or the address of an operand. The 12-bit
length allows the direct addressing of 4096 bytes
in Program space.

Figure 6. ST6 Core Block Diagram

PROGRAM

RESET

OPCODE

FLAG

VALUES

2

CONTROLLER

FLAGS

ALU

A-DATA

B-DATA

ADDRESS/READ LINE

DATA SPACE

INTERRUPTS

DATA

RAM/EEPROM

DATA

ROM/EPROM

RESULTS TO DATA SPACE (WRITE LINE)

ROM/EPROM

DEDICATIONS

ACCUMULATOR

CONTROL

SIGNALS

OSCin

OSCout

ADDRESS

DECODER

256

12

Program Counter

and

6 LAYER STACK

0,01 TO 8MHz

VR01811

15

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ST62T45B/E45B

CPU REGISTERS(Cont’d)

However, if the program space contains more
than 4096 bytes, the additional memory in pro­gram space can be addressed by using the Pro­gram Bank Switch register.

The PC value is incremented after reading the ad­dress of the current instruction. To execute rela­tive jumps, the PC and the offset are shifted
through the ALU, where they are added; the result
is then shifted back into the PC. The program
counter can be changed in the following ways:

- JP (Jump) instructionPC=Jump address

- CALL instructionPC= Call address

- Relative Branch Instruction.PC= PC +/- offset

- Interrupt PC=Interrupt vector

- Reset PC= Reset vector

- RET & RETI instructionsPC= Pop (stack)

- Normal instructionPC= PC + 1

Flags (C, Z).The ST6 CPU includes three pairs of
flags (Carry and Zero), each pair being associated
with one of the three normal modes of operation:
Normal mode, Interrupt mode and Non Maskable
Interrupt mode. Each pair consists of a CARRY
flag and a ZERO flag. One pair (CN, ZN) is used
during Normal operation, another pair is used dur­ing Interrupt mode (CI, ZI), and a third pair is used
in the Non Maskable Interrupt mode (CNMI, ZN­MI).

The ST6 CPU uses the pair of flags associated
with the current mode: as soon as an interrupt (or
a Non Maskable Interrupt) is generated, the ST6
CPU uses the Interrupt flags (resp. the NMI flags)
instead of the Normal flags. When the RETI in­struction is executed, the previously used set of
flags is restored. It should be noted that each flag
set can only be addressed in its own context (Non
Maskable Interrupt, Normal Interrupt or Main rou­tine). The flags are not cleared during context
switching and thus retain their status.

The Carry flag is set when a carry or a borrow oc­curs during arithmetic operations; otherwise it is
cleared. The Carry flag is also set to the value of
the bit tested in a bit test instruction; it also partic­ipates in the rotate left instruction.

The Zero flag is set if the result of the last arithme­tic or logical operation was equal to zero; other­wise it is cleared.

Switching between the three sets of flags is per­formed automatically when an NMI, an interrupt or
a RETI instructions occurs. As the NMI mode is

automatically selected after the reset of the MCU,
the ST6 core uses at first the NMI flags.

Stack. The ST6 CPU includes a true LIFO hard­ware stack which eliminates the need for a stack
pointer. The stack consists of six separate 12-bit
RAM locations that do not belong to the data
space RAM area. When a subroutine call (or inter­rupt request) occurs, the contents of each level
are shifted into the next higher level, while the
content of the PC is shifted into the first level (the
original contents of the sixth stack level are lost).
When a subroutine or interrupt return occurs (RET
or RETI instructions), the first level register is shift­ed back into the PC and the value of each level is
popped back into the previous level. Since the ac­cumulator, in common with all other data space
registers, is not stored in this stack, management
of these registers should be performed within the
subroutine. The stack will remain in its “deepest”
position if more than 6 nested calls or interrupts
are executed, and consequently the last return ad­dress will be lost. It will also remain in its highest
position if the stack is empty and a RET or RETI is
executed. In this case the next instruction will be
executed.

Figure 7. ST6 CPU Programming Mode

l

SHORT

DIRECT

ADDRESSING

MODE

VREGISTER

W REGISTER

PROGRAM COUNTER

SIX LEVELS

STACK REGISTER

CZNORMALFLAGS

INTERRUPTFLAGS

NMI FLAGS

INDEX

REGISTER

VA000423

b7

b7

b7

b7

b7

b0

b0

b0

b0

b0

b0b11

ACCUMUL ATOR

YREG.POINTER

XREG.POINTER

CZ

CZ

16

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ST62T45B/E45B

3 CLOCKS, RESET, INTERRUPTS AND POWER SAVING MODES

3.1 CLOCK SYSTEM

3.1.1 Main Oscillator

The MCU features a Main Oscillator which can be
driven by an external clock, or used in conjunction
with an AT-cut parallel resonant crystal or a suita­ble ceramic resonator.

Figure 8 illustrates various possible oscillator con­figurations usingan external crystalorceramic res­onator, an external clock input. CL1an CL2should
have a capacitance in the range 12 to 22 pF for an
oscillator frequency in the 4-8 MHz range.

The internal MCU clock Frequency (F

INT

) is divid­ed by 13 to drive the CPU core and by 12 to drive
the A/D converter and the watchdog timer, while
clock used to drive on-chip peripherals depends
on the peripheral as shown in the clock circuit
block diagram.

With an 8MHz oscillator frequency, the fastest
machine cycle is therefore 1.625µs.

A machine cycle is thesmallest unit of timeneeded
toexecute any operation (for instance,to increment
the Program Counter). An instruction may require
two, four, or five machine cycles for execution.

Figure 8. Oscillator Configurations

Figure 9. Clock Circuit Block Diagram

OSC

in

OSC

out

C

L1n

C

L2

ST6xxx

CRYSTAL/RESONATORCLOCK

OSC

in

OSC

out

ST6xxx

EXTERNAL CLOCK

NC

VA0016

VA0015A

MAIN

OSCILLATOR

Core

:13

:12

Timer 1 & 2

Watchdog

POR

f

INT

ADC

OSCin

OSCout

f

OSC

f

INT

OSC32in

OSC32out

32kHz

OSCILLATOR

MUX

LCD
CONTROLLER
DRIVER

EOCR bit 5

(START/STOP)

17

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ST62T45B/E45B

CLOCK SYSTEM (Cont’d)

3.1.2 32kHz STAND-BY OSCILLATOR

An additional 32kHz stand-by on chip oscillator al­lows to generate real time interrupts and to supply
the clock to the LCD driver with the main oscillator
stopped. This enables the MCU to perform real
time functions with the LCD display running while
keeping advantages of low power consumption.
Figure 10 shows the 32kHz oscillator block dia­gram.

A 32.768kHz quartz crystal must be connected to
the OSC32in and OSC32out pins to perform the
real time clock operation. Two external capacitors
of 15-22pF each must be connected between the
oscillator pins and ground. The 32kHz oscillator is
managed by the dedicated status/control register
32OCR.

As long as the 32kHz stand-by oscillator is ena­bled, 32kHz internal clock is available to drive
LCD controller driver. This clock is divide by 214to
generate interrupt request every 500ms . The pe­riodic interrupt request serves as reference time­base for real time functions.

Note

: When the 32kHz stand-by oscillator is
stopped (bit 5 of the Status/Control register
cleared) the divider chain is supplied with a clock
signal synchronous with machine cycle (f

INT

/13),

this produces an interrupt request every 13x2

14

clock cycle (i.e. 26.624ms) with an 8MHz quartz
crystal.

32kHz Oscillator Register (32OCR)

Address: DBh - Read/Write

Bit 7 = EOSCI.

Enable Oscillator Interrupt

.This
bit, when set, enables the 32kHz oscillator inter­rupt request.

Bit 6 = OSCEOC.

Oscillator Interrupt Flag

. This bit
indicates when the 32kHz oscillator has measured
a 500ms elapsed time (providing a

32.768kHzquartz crystal is connected to the
32kHz oscillator dedicated pins). An interrupt re­quest can be generated in relation to the state of
EOSCI bit. This bit must be cleared by the user
program before leaving the interrupt service rou­tine.

Bit 5 =

START/STOP

.O

scillator Start/Stop bit

.
This bit, when set, enables the 32kHz stand-by os­cillator and the free running divider chain is sup­plied by the 32kHz oscillator signal. When this bit
is cleared to zero the divider chain is supplied with
f

INT

/13.

This register is cleared during reset.

Note

:

To achieve minimum power consumption in STOP
mode (no system clock), the stand-by oscillator
must be switched off (real time function not availa­ble) by clearing the Start/Stop bit in the oscillator
status/control register.

Figure 10. 32kHz Oscillator Block Diagram

70

EOSCI OSCEOC S/S D4 D3 D2 D1 D0

OSC32KHz

EOSCI OSCEOC

START

STOP

XX XXX

INT

OSC32IN

OSC32OUT

2x15...22pF

32.768kHz
Crystal

f

INT

/13

OSC32KHz MUX

1
0

DIV 2

14

18

20/72

ST62T45B/E45B

3.2 RESETS

The MCU can be reset in three ways:
– by the external Reset input being pulled low;
– by Power-on Reset;
– by the digital Watchdog peripheral timing out.

3.2.1 RESET Input

The RESET pin may be connected to a device of
the application board in order to reset the MCU if
required. The RESET pin may be pulled low in
RUN, WAIT or STOP mode. This input can be
used to reset the MCU internal state and ensure a
correct start-up procedure. The pin is active low
and features a Schmitt trigger input. The internal
Reset signal is generated by adding a delay to the
external signal. Therefore even short pulses on
the RESET pin are acceptable, provided VDDhas
completed its rising phase and that the oscillator is
running correctly (normal RUN or WAIT modes).
The MCU is kept in the Reset state as long as the
RESET pin is held low.

If RESET activation occurs in the RUN or WAIT
modes, processing of the user program is stopped
(RUN mode only), the Inputs and Outputs are con­figured as inputs with pull-up resistors and the
main Oscillator is restarted. When the level on the
RESET pin then goes high, the initialization se­quence is executed following expiry of the internal
delay period.

If RESET pin activation occurs in the STOP mode,
the oscillator starts up and all Inputs and Outputs
are configured as inputs with pull-up resistors.
When the level of theRESET pin then goes high,
the initialization sequence is executed following
expiry of the internal delay period.

3.2.2 Power-on Reset

The function of the POR circuit consists in waking
up the MCU at an appropriate stage during the
power-on sequence. At the beginning of this se­quence, the MCU is configured in the Reset state:
all I/O ports are configured as inputs with pull-up
resistors and no instruction is executed. When the
power supply voltage rises to a sufficient level, the
oscillator starts to operate, whereupon an internal
delay is initiated, in order to allow the oscillator to
fully stabilize before executing the first instruction.
The initialization sequence is executed immedi­ately following the internal delay.

The internal delay isgenerated by anon-chip coun­ter. The internal reset line is released 2048 internal
clock cycles after release of the external reset.

Notes:

To ensure correct start-up, the user should take
care that the reset signal is not released before
the VDDlevel is sufficient to allow MCU operation
at the chosen frequency (see Recommended Op­erating Conditions).

A proper reset signal for a slow rising VDDsupply
can generally be provided by an external RC net­work connected to theRESET pin.

Figure 11. Reset and Interrupt Processing

INT LATCH CLEARED

NMI MASK SET

RESET

( IF PRESENT )

SELECT

NMI MODE FLAGS

IS RESET STILL

PRESENT?

YES

PUT FFEH

ON ADDRESS BUS

FROMRESET LOCATIONS

FFE/FFF

NO

FETCH INSTRUCTION

LOAD PC

VA000427

19

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ST62T45B/E45B

RESETS (Cont’d)

3.2.3 Watchdog Reset

The MCU provides a Watchdog timer function in
order to ensure graceful recovery from software
upsets. If the Watchdog register is not refreshed
before an end-of-count condition is reached, the
internal reset will be activated. This, amongst oth­er things, resets the watchdog counter.

The MCU restarts just as though the Reset had
been generated by the RESET pin, including the
built-in stabilisation delay period.

3.2.4 Application Notes

No external resistor is required between VDDand
the Reset pin, thanks to the built-in pull-up device.

The POR circuit operates dynamically, in that it
triggers MCU initialization on detecting the rising
edge of VDD. The typical threshold is in the region
of 2 volts, but the actual value of the detected
threshold depends on the way in which VDDrises.

The POR circuit is

NOT

designed to supervise

static, or slowly rising or falling VDD.

3.2.5 MCU Initialization Sequence

When a reset occurs the stack is reset, the PC is
loaded with the address of the Reset Vector (lo­cated in program ROM starting at address
0FFEh). A jump to the beginning of the user pro­gram must be coded at this address. Following a

Reset, the Interrupt flag is automatically set, so
that the CPU is in Non Maskable Interrupt mode;
this prevents the initialisation routine from being
interrupted. The initialisation routine should there­fore be terminated by a RETI instruction, in order
to revert to normal mode and enable interrupts. If
no pending interrupt is present atthe end of the in­itialisation routine, the MCU will continue by
processing the instruction immediately following
the RETI instruction. If, however, a pending inter­rupt is present, it will be serviced.

Figure 12. Reset and Interrupt Processing

Figure 13. Reset Block Diagram

RESET

RESET

VECTOR

JP

JP:2 BYTES/4 CYCLES

RETI

RETI: 1 BYTE/2 CYCLES

INITIALIZATION

ROUTINE

VA00181

V

DD

RESET

300kΩ

2.8kΩ

POWER

WATCHDOG RESET

CK

COUNTER

RESET

ST6
INTERNAL
RESET

f

OSC

RESET

ON RESET

VA0200B

20

22/72

ST62T45B/E45B

RESETS (Cont’d)
Table 6. Register Reset Status

Register Address(es) Status Comment

EEPROM Control Register
Port Data Registers
Port A,B Direction Register
Port A,B Option Register
Interrupt Option Register

SPI Registers
LCD Mode Control Register
32kHz Oscillator Register

0DFh
0C0h, 0C2h, 0C3h
0C4h to 0C5h
0CCh, 0CEh
0C8h

0C2h to 0DDh
0DCh
0DBh

00h

EEPROM enabled

I/O are Input with pull-up

Interrupt disabled

SPI disabled
LCD display off
Interrupt disabled

Port C Direction Register
Port C Option Register

0C6h
0CFh

FFh LCD Output

X, Y,V, W, Register
Accumulator
Data RAM
Data RAM Page REgister
Data ROM Window Register
EEPROM
A/D Result Register

080H TO083H
0FFh
084h to 0BFh
0CBh
0C9h
00h to 03Fh
0D0h

Undefined As written if programmed

TIMER 1 Status/Control
TIMER 1 Counter Register
TIMER 1 Prescaler Register

TIMER 2 Status/Control
TIMER 2 Counter Register
TIMER 2 Prescaler Register

Watchdog Counter Register
A/D Control Register

0D4h
0D3h
0D2h

0D7h
0D5h
0D6h

0D8h
0D1h

00h
FFh
7Fh

00h
FFh
7Fh

FEh

40h

TIMER 1 disabled/Max count loaded

TIMER 2 disabled/Max count loaded

A/D in Standby

21