NEC UPD6708GS, UPD6708CX Datasheet

DATA SHEET

MOS INTEGRATED CIRCUIT

PD6708

IEBus (Inter Equipment Bus) PROTOCOL CONTROL LSI

DESCRIPTION

The µPD6708 is a peripheral LSI for microcontrollers that controls the protocol of the IEBus.

This LSI processes the protocol of the IEBus. Because it is provided with a transmit/receive buffer, the microcontroller can concentrate on the application processing of the IEBus. Because the µPD6708 also contains an IEBus driver/receiver, it can be directly connected to the bus.

FEATURES

• Protocol control of IEBus

• Multi-master system

• Broadcast communication function (communication between one unit and multiple units)

• Choice of three modes with different transmission speeds

At 12 MHz At 12.58 MHz Mode 0 Approx. 3.9 Kbps Approx. 4.1 Kbps Mode 1 Approx. 17 Kbps Approx. 18 Kbps Mode 2 Approx. 26 Kbps Approx. 27 Kbps

• On-chip IEBus driver/receiver

• Transmit/receive buffer

Transmit: 4-byte FIFO Receive: 20-byte FIFO

• Interface with microcontroller

• Three-line serial I/O (SCK, SO, SI pins)

• Transfer with MSB first

• Oscillation frequency (f

• In modes 0 and 1: ±1.5 %

• In mode 2: ±0.5 %

• Supply voltage: V

X): 12 MHz, 12.58 MHz

DD = 5 V ±10 %

ORDERING INFORMATION

Part Number Package

PD6708CX 16-pin plastic DIP (300 mil)

PD6708GS 16-pin plastic SOP (300 mil)

APPLICATION FIELD

Fields where a small-scale digital data transfer system is required between equipment, such as automobile electronic

systems and industrial equipment

Document No. U10680EJ2V0DS00 (2nd edition) (Previous No. IC-3282) Date Published January 1996 P Printed in Japan

The information in this document is subject to change without notice.

The mark ★ shows major revised points.

1993

PIN CONFIGURATION (TOP VIEW)

• 16 pin plastic DIP (300 mil)

PD6708CX

• 16 pin plastic SOP (300 mil)

PD6708GS

PD6708

SCK

IRQ

R/W

GND

TEST

RESET

C/D

BUS+

BUS–

SCK : Serial clock input SI : Serial data input SO : Serial data output IRQ : Interrupt request output R/W : Read/write switchover input XI, XO : System clock GND : Ground BUS–, BUS+ : IEBus input/output AVDD : IEBus analog power supply (connected to VDD pin) C/D : Command/data switchover input CS : Chip select input RESET : Reset input TEST : Test input (connected to VDD pin)

DD : Positive power supply

PD6708

CONTENTS

1. PIN FUNCTIONS......................................................................................................................................... 5

1.1 List of Pin Functions ......................................................................................................................................... 5

2. IEBus OPERATION .................................................................................................................................... 6

2.1 Operation Overview ........................................................................................................................................... 6

2.2 IEBus Communication Protocol ...................................................................................................................... 7

2.2.1 Bus mastership determination (arbitration) ................................................................................... 8

2.2.2 Communication modes ...................................................................................................................... 8

2.2.3 Communication address ................................................................................................................... 9

2.2.4 Broadcast communication ................................................................................................................ 9

2.3 Transfer Protocol ............................................................................................................................................. 10

2.4 Transfer Data (Contents of Data Field)......................................................................................................... 16

2.5 Bit Format ......................................................................................................................................................... 19

3. INTERNAL CONFIGURATION................................................................................................................. 20

3.1 Data Link Layer Controller ............................................................................................................................. 21

3.2 Physical Layer Controller ............................................................................................................................... 21

3.3 IEBus Driver/Receiver ..................................................................................................................................... 2 1

3.4 Host Interface ................................................................................................................................................... 21

4. INTERFACING WITH HOST CONTROLLER .......................................................................................... 22

4.1 Accessible Buffers and Registers from Host Controller ........................................................................... 22

4.1.1 Write data buffer (WDB) .................................................................................................................. 22

4.1.2 Read data buffer (RDB) ................................................................................................................... 2 2

4.1.3 Command register (CMR)................................................................................................................ 22

4.1.4 Status register (STR) ....................................................................................................................... 23

4.2 Host Interface Modes ...................................................................................................................................... 23

4.2.1 Switching through pin control ....................................................................................................... 24

4.2.2 Switching through software control.............................................................................................. 26

4.3 Reset Mode ....................................................................................................................................................... 28

5. COMMUNICATION CONTROL COMMANDS ......................................................................................... 30

5.1 Overview of Communication Control Commands....................................................................................... 30

5.2 Communication Control Command Functions............................................................................................ 31

5.2.1 INIT command (command code: 0000) .......................................................................................... 31

5.2.2 SETSA command (command code: 0001) .................................................................................... 32

5.2.3 MREQ1 command (command code: 0010) ................................................................................... 33

5.2.4 MREQ2 command (command code: 0011) ................................................................................... 34

5.2.5 ABORT command (command code: 0100) ................................................................................... 34

5.2.6 SETSD command (command code: 0101) .................................................................................... 35

5.2.7 GETSTA command (command code: 0110).................................................................................. 36

5.2.8 SETREV command (command code: 0111).................................................................................. 37

6. RETURN CODES...................................................................................................................................... 38

6.1 Return Codes in Master/Slave Data Transmission ..................................................................................... 38

6.2 Return Codes in Master Reception ............................................................................................................... 38

6.3 Return Codes in Slave Reception ................................................................................................................. 39

6.4 Return Codes in Broadcast Reception ......................................................................................................... 39

6.5 Return Codes Generation Intervals............................................................................................................... 40

7. COMMUNICATING WITH HOST CONTROLLER ................................................................................... 43

7.1 Master Transmission ....................................................................................................................................... 43

7.1.1 Master transmission by MREQ1 command .................................................................................. 43

7.1.2 Master transmission by MREQ2 command .................................................................................. 44

PD6708

7.2 Slave Transmission ......................................................................................................................................... 44

7.2.1 Data transmission ............................................................................................................................ 44

7.2.2 Transmitting slave status address and lock address................................................................. 45

7.3 Master Reception ............................................................................................................................................. 45

7.4 Slave Reception ............................................................................................................................................... 46

7.5 Broadcast Reception ....................................................................................................................................... 47

8. EXAMPLE OF HOST CONTROLLER PROCESSING FLOW ................................................................48

8.1 Main Routine..................................................................................................................................................... 48

8.2 Interrupt Service Routine ................................................................................................................................49

8.3 Processing Routine ......................................................................................................................................... 50

8.3.1

8.3.2 Communication control command processing routine.............................................................. 51

8.3.3 Master transmission processing routine...................................................................................... 57

8.3.4 Slave data transmission processing routine ............................................................................... 58

8.3.5 Master reception processing routine ............................................................................................ 5 9

PD6708 initialization routine......................................................................................................... 50

9. ELECTRICAL SPECIFICATIONS ............................................................................................................ 63

10. PACKAGE DRAWINGS............................................................................................................................ 6 7

11. RECOMMENDED SOLDERING CONDITIONS....................................................................................... 69

APPENDIX MAJOR DIFFERENCES BETWEEN µPD6708 AND µPD72042A, µPD72042B ................... 70

PD6708

1. PIN FUNCTIONS

1.1 List of Pin Functions

Pin No. Pin Name Input/Output Function I/O Format At Reset

1 SCK Input Input for serial clock used to interface with microcontroller. CMOS input Input 2 SI Input Input for serial data used to interface with microcontroller. CMOS input Input 3 SO Output Output for serial data used to interface with microcontroller. CMOS output High level 4 IRQ Output Output used by interrupt request signals generated by CMOS output Low level

communication and command execution results. Used as operation start request signal to microcontroller. The interrupt request signal is output for 8 µs or longer at high level.

5 R/W Input Input for switching serial interface read/write mode. CMOS input Input

When high, it is in the read mode. When low, it is in the write mode. When this pin is low and C/D pin high, the read and write modes can be switched by commands input from the serial interface.

6 XI –– Connection pins for system clock resonator. –– (Oscillation 7 XO Use a 12- or 12.58-MHz crystal, or ceramic resonator. continues)

Frequency precision depends on the communication mode used.

Mode 0 : ±1.5 % Mode 1 : ±1.5 %

Mode 2 : ±0.5 % 8 GND –– Ground –– –– 9 BUS– Input/output Input/output for IEBus. –– High

10 BUS+ impedance 11 AVDD –– 12 C/D Input Input used to switch between processing data input to the CMOS input Input

13 CS Input Chip select input. CMOS input Input

IEBus driver/receiver analog power supply. Connect to VDD.

serial interface as commands or data. When set to high, data is processed as commands; when low, data is processed as data. When this pin is high and R/W pin low, the read and write modes can be switched by commands input from the serial interface.

When low, serial interface input is enabled. When high, serial clock (SCK) input is disabled, SO pin becomes high impedance, and the serial clock counter is reset. The status of CS pin is not affected by IEBus transmit and receive operations.

–– ––

14 RESET Input System reset signal input pin. CMOS input Input

Low input effects a reset. Always input the low signal for 6 µs or longer after turning

on the power. 15 TEST Input Always connect this pin to the VDD. CMOS input –– 16 VDD –– Positive power supply input. Apply a voltage of 5 V ±10 %. –– ––

PD6708

2. IEBus OPERATION

2.1 Operation Overview

★

The

PD6708 is an IEBus interface CMOS LSI device. The IEBus is a bus for a small-scale digital data transfer system designed to transfer data between electronic devices. The µPD6708 is connected to a microcontroller incorporated in electronic equipment with a serial interface (SCK, SO,

SI pins). The data and commands required to transfer data with the host controller (microcontroller) are set via this serial interface.

When the host controller transmits data to the

(BUS+ and BUS–). Data received from the BUS pins can be read by the host controller via the serial interface.

PD6708 via the serial interface, signals are output from the BUS pins

PD6708

2.2 IEBus Communication Protocol

An overview of the IEBus is as follows.

• Communication system: Half-duplex asynchronous communication

• Multi-master system All the units connected to the IEBus can transfer data to the other units.

• Broadcast communication function (communication between one unit and multiple units) Group broadcast communication: Broadcast communication with group units General broadcast communication: Broadcast communication with all units.

• Three modes with different transfer speeds selectable.

fX = 12 MHz fX = 12.58 MHz Maximum Number of Transfer Bytes

(bytes/frame) Mode 0 Approx. 3.9 Kbps Approx. 4.1 Kbps 16 Mode 1 Approx. 17 Kbps Approx. 18 Kbps 32 Mode 2 Approx. 26 Kbps Approx. 27 Kbps 128

• Access control: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) The priority order for bus occupancy is as follows.

★

<1> Broadcast communication takes precedence over ordinary communication (i. e., communication between one

unit and another).

<2> The lowest master address has the highest priority.

• Communication scale Number of units: MAX. 50 Cable length: MAX. 150 m (with twisted-pair cable <Resistance: 0.1 Ω/m or less>) Load capacity: MAX. 8000 pF <between BUS– and BUS+>, fX = 12 MHz

MAX. 7100 pF <between BUS– and BUS+>, f

Terminating resistor: 120 Ω

X = 12.58 MHz

PD6708

2.2.1 Bus mastership determination (arbitration)

When a unit connected to the IEBus controls another unit, it performs an operation to occupy the bus. This operation

★

is called arbitration.

Arbitration is to select one unit, and if several units begin to transmit data simultaneously, gives permission to occupy

the bus to that one unit.

So that one unit is granted the permission to occupy the bus as a result of the arbitration, the following priority conditions

are determined.

Remark The units not given permission through arbitration are automatically allowed to get into retransfer mode (number

of retransfer times for the

PD6708: 3).

(1) Priority according to type of communication

Broadcast communication (between a single and multiple units) takes precedence over ordinary communication

(between single units).

(2) Priority according to master address

If the communication devices are of the same type, the unit with the lowest master address has the highest priority.

Example The master address comprises 12 bits, and unit 000H has the highest priority while unit FFFH has the lowest

priority.

2.2.2 Communication modes

The IEBus is provided with three communication modes with different transfer speeds. The transfer speed and maximum

number of transfer bytes in a single communication frame in each communication mode are shown in Table 2-1.

Table 2-1. Transfer Speed and Maximum Number of Transfer Bytes in Each Communication Mode

Communication Mode Maximum Number of Transfer Bytes (bytes/frame) Actual Transfer Speed

fX = 12 MHz 0 16 Approx. 3.9 Approx. 4.1 1 32 Approx. 17 Approx. 18 2 128 Approx. 26 Approx. 27

Note 2

Note 1

(Kbps)

fX = 12.58 MHz

Note 2

Notes 1. Actual transfer speed when the maximum number of bytes is transferred

2. Oscillation frequency when the

PD6708 is used

Cautions 1. A communication mode is selected for each unit connected to the IEBus before communication is

performed. If the communication mode of the master unit is not the same as that of the unit with which the master unit is to communicate (slave unit), communication cannot be performed correctly.

2. If the oscillation frequency of one unit is fx = 12 MHz and that of the other unit is fx = 12.58 MHz,

communication cannot be performed correctly even if the communication mode is the same. Make sure that the oscillation frequencies of the two units to communicate are the same.

PD6708

2.2.3 Communication address

With the IEBus, a 12-bit communication address is assigned to each unit. The communication address is made up as

follows.

Higher 4 bits: Group number (number which identifies the group to which the unit belongs) Lower 4 bits: Unit number (number which identifies a unit within a group)

2.2.4 Broadcast communication

In ordinary communication, there is only one master unit and one slave unit, and transmission or reception is performed on an one-to-one basis. In broadcast communication, however, there are a number of slave units and the master unit performs transmission with these slave units. Because there are several slave units, no acknowledge signals is returned from the slave units during communication.

Whether broadcast communication or ordinary communication is performed is specified by the broadcast bit (for the broadcast bit, see 2.3 (1) <2> “Broadcast bit”).

There are two kinds of broadcast communication, as follows.

(1) Group broadcast communication

Broadcast communication is performed to the units in a group whose group numbers are the same as that specified by the higher 4 bits of the communication address.

★

(2) General broadcast communication

Broadcast communication is performed to all units irrespective of their group numbers.

Group broadcast communication or general broadcast communication is identified by the value of a salve address (for the slave address, see 2.3 (3) “Slave address field”).

PD6708

2.3 Transfer Protocol

The IEBus transfer signal format is shown in Figure 2-1.

Data is transferred as a series of signals called a communication frame. The number of data that can be transferred in one communication frame and the transfer speed differ depending on the communication mode.

Figure 2-1. Transfer Signal Format

(fx = at 12 MHz)

★

Field Name

Number of Bits

Transfer Time

Header

Start

Bit

Broad-

cast

Master

Address Field

1121 112 11411811811 811

Master

Address

Bit

Slave Address

P Slave

Address

Field

P A Control

Control Field Message

Bit

Length Field

Message

Length

Bit

P A Data

Data Field

P A Data

Bit

Mode 0

Mode 1 Mode 2

Approx. 7330 s

Approx. 2090 s

Approx. 1590 s

µ µ µ

Approx. 1590 × N s

Approx. 410 × N s

Approx. 300 × N s

µ µ µ

P: Parity bit (1 bit) A: Acknowledge bit (1 bit)

When A = 0: ACK When A = 1: NAK

N: Number of data bytes

Remark In broadcast communication, the value of the acknowledge bit is ignored.

(1) Header

A header comprises a start bit and a broadcast bit, as described below.

<1> Start bit

The start bit is a signal which tells the other units that data transmission will start. The unit which is about to start transmitting data will output the low signal (the start bit) for a specified time, and then

outputs the broadcast bit.

If another unit is already outputting a start bit before one unit outputs a start bit, the unit will not output the start bit.

It will wait until the another unit completely outputs the start bit, and then outputs the broadcast bit.

The units other than the one that has started transmission detect this start bit and enters the reception state.

<2> Broadcast bit

The broadcast bit distinguishes between broadcast communication and ordinary communication.

When this bit is ‘0’, it indicates broadcast communication; when it is ‘1’, it indicates ordinary communication. There are two types of broadcast communication: group broadcast and general broadcast. These types are identified by the value of the slave address (for the slave address, see (3) “Slave address field”).

In broadcast communication, there are a number of slave units. Therefore, the acknowledge bit is not returned in the fields described in (2) below and onward.

If two or more units start to transmit a communication frame simultaneously, broadcast communication takes precedence over ordinary communication, and wins in the arbitration.

PD6708

(2) Master address field

The master address field is used to transmit the unit address of the master unit (master address) to the other units. The master address field consists of master address bits and a parity bit. The master address comprises 12 bits and is output from the MSB. If two or more units start transmitting the broadcast bit of the same value simultaneously, the arbitration decision is made

by the master address field.

The master address field compares the data the master has output with the data on the bus each time the master transmits

1 bit of data. If the master address output by the master unit is different from the data on the bus, the master unit assumes that it has lost in arbitration, stops transmission, and enters the reception state.

Because the IEBus has a wired-AND configuration, the unit having the lowest master address of the units participating

in the arbitration (arbitration masters) wins in the arbitration. Ultimately, only one unit remains in the transmission state as the master unit after outputting a 12-bit master address.

This master unit then outputs a parity bit

slave address field.

Note Even parity is used. When the number of the bits that are ‘1’ in the master address is odd, the parity bit is ‘1’.

(3) Slave address field

The slave address field is used to transmit the address (slave address) of a unit (slave unit) with which the master wishes

to communicate.

The slave address field consists of slave address bits, a parity bit, and an acknowledge bit. The slave address comprises 12 bits and is output from the MSB. After the 12-bit slave address is transmitted, the parity

bit is output to prevent the slave address from being received incorrectly. Next, the master unit looks for the acknowledge signal (bit) from the slave unit to confirm that the slave unit exists on the bus. When the master unit detects the acknowledge signal, it starts outputting the control field. In the case of broadcast communication, however, the master unit outputs the control field without waiting for the acknowledge bit.

A slave unit outputs the acknowledge signal if it has detected that its slave address coincides with that selected by the

master and that the parities of both the master and slave addresses are even. If the parity is odd, the slave unit assumes that the master or slave address has not been correctly received, and does not output the acknowledge signal. In this case, the master unit enters the standby (monitor) state and communication ceases.

In the case of broadcast communication, the slave address is used to distinguish between group broadcast and general

broadcast as follows:

Note

, makes the other units confirm the master address, and then outputs the

★

Slave address = FFFH: General broadcast communication Slave address ≠ FFFH: Group broadcast communication

Remark In the case of group broadcast communication, the group number is the value of higher 4 bits of the slave

address.

PD6708

(4) Control field

★

The control field indicates the type of data and the transfer direction of the subsequent data field. The control field consists of 4 control bits, a parity bit, and an acknowledge bit. The control bits are output from the MSB. A parity bit is output after the control bits. When the parity is even and the slave can execute the function requested

by the master unit, the slave unit outputs an acknowledge signal, and then outputs the next message length field. If the slave unit cannot execute the function requested by the master unit even if the parity is even, or if the parity is odd, the slave unit does not output the acknowledge signal but returns to the standby (monitor) state.

After the master unit has confirmed the acknowledge signal, it starts outputting the next message length field. If the master unit is cannot confirm the acknowledge signal, it enters the standby state and stops communication. In

the case of broadcast communication, however, the master unit starts outputting the message length field without confirming the acknowledge signal.

For the functions of the control bits, see Table 2-3.

(5) Message length field

The message length field is used to specify the number of communication data bytes. The message length field comprises 8 message length bits, a parity bit and, an acknowledge bit. The message length bits are output from the MSB. The message length bits indicate the number of communication data

bytes as shown in Table 2-2.

Table 2-2. Meaning of Message Length Bits

Message Length Bits (hex) Number of Transmission Data Bytes

01H 1 byte 02H 2 bytes

:: FFH 255 bytes 00H 256 bytes

Remark In the communication mode, if the number of bytes exceeding the maximum number of transfer bytes per frame

is set, two or more frames are communicated. In this case, the message length bits indicate the number of remaining communication data bytes during the second communication and onward.

The operation of this field differs depending on whether the master transmits (bit 3 of control bits is 1) or receives (bit

3 of control bits is 0) data.

<1> When master transmits data

The message length bits and parity bit are output by the master unit. The slave unit outputs the acknowledge signal and then the next data field if it detects that the parity is even. The slave unit does not output the acknowledge signal in the case of broadcast communication.

If the parity is odd, the slave unit assumes that the message length bits have not been received correctly, and returns to the standby (monitor) state without outputting the acknowledge signal. In this case, the master unit also returns to the standby state, and communication ceases.

PD6708

<2> When master receives data

The message length bits and parity bit are output by the slave unit. The master unit outputs the acknowledge signal if it detects that the parity bit is even.

If the parity is odd, the master unit assumes that the message length bits have not been received correctly, and returns to the standby state without outputting the acknowledge signal. In this case, the slave unit also returns to the standby state, and communication ceases.

(6) Data field

The data field is used to transmit/receive data to/from the slave units. The master unit uses the data field to transmit data to and receive data from the slave units. The data field consists of 8 data bits, a parity bit, and an acknowledge bit. The data bits are output from the MSB. Following the data bits, the parity bit and acknowledge bit are output from the master unit and the slave unit, respectively. Broadcast communication is performed when only the master unit transmits data. At this time, the acknowledge signal

is ignored.

The operation differs depending on whether the master performs transmission or reception, as follows.

<1> When master transmits data

When the master unit writes data to the slave unit, the master unit transmits data bits and a parity bit to the slave unit. The slave unit receives the data bits and parity bit. If the parity is even and the receive buffer is empty, the slave unit outputs the acknowledge signal. If the parity is odd and the receive buffer is not empty, the slave unit denies acknowledgment of the corresponding data and does not output the acknowledge signal.

If no acknowledge signal is output from the slave unit, the master unit transmits the same data again. The master unit continues this operation until it detects the acknowledge signal from the slave unit or the data reaches the maximum number of transfer bytes.

If the parity is even and the acknowledge signal has been output from the slave unit, and if the master unit has more data to transmit and the maximum number of transfer bytes is not exceeded, the master unit will transmit the next data.

In the case of broadcast communication, the slave unit does not output the acknowledge signal, and the master unit transfers data on a byte-by-byte basis.

★

<2> When master receives data

When the master unit reads data from the slave unit, the master unit outputs synchronization signals corresponding to all the read bits.

The slave unit outputs the contents of the data and parity bits onto the bus in accordance with the synchronization signals from the master unit.

The master unit reads the data and parity bit output by the slave unit, and checks the parity.

If the parity is odd or the receive buffer is not empty, the master unit denies acknowledgement of that data and does not output the acknowledge signal. If the data is within the maximum number of transfer bytes that can be transmitted in one frame, the master unit repeatedly reads the same data.

If the parity is even and the receive buffer is empty, the master unit acknowledges the data and transmits back the acknowledge signal. If the data is within the maximum number of bytes that can be transmitted in one frame, the master unit reads the next data.

★

PD6708

(7) Parity bits

Parity bits are used to check that there is no error in the transfer data. A parity bit is added to the master address bits, slave address bits, control bits, message length bits, and data bits. Even parity is used. If the number of the bits that are ‘1’ bits in data is odd, the parity bit is ‘1’, and if the number of the

bits that are ‘1’ bits is even, the parity bit is ‘0’.

(8) Acknowledge bits

In ordinary communication (between two units), an acknowledge bit is added to the following places to confirm that data

has been acknowledged correctly.

• At the end of the slave address field.

• At the end of the control field.

• At the end of the message length field.

• At the end of a data field.

The definition of the acknowledge bit is as follows.

• ‘0’: Indicates that transfer data has been acknowledged (ACK).

• ‘1’: Indicates that transfer data has not been acknowledged (NAK).

Note that the value of the acknowledge bit is ignored in broadcast communication.

<1> Acknowledge bit at the end of the slave field

When any of the following conditions is met, the acknowledge bit at the end of the slave field is NAK, and communication is discontinued.

• If the parity of the master address bits or slave address bits is incorrect.

• If a timing error (error in bit format) occurs.

• If the slave unit does not exist.

<2> Acknowledge bit at the end of the control field

When any of the following conditions is met, the acknowledge bit at the end of the control field is NAK, and communication is discontinued.

• If the parity of the control bits is incorrect.

★

• If bit 3 of the control bits is ‘1’ (write operation) when the slave receive buffer

• If the control bits indicate read operation (3H or 7H) when the slave transmit buffer

• If 3H, 6H, 7H, AH, BH, EH, or FH of control bits is requested from a unit other than the unit which set the lock when a lock has been set.

• If the control bits indicate lock address read (4H) when a lock has not been set.

• If a timing error occurs.

• If the control bits are undefined.

Note

is not empty.

Note

is empty.

Note See 2.4 (1) “Reading slave status (SSR) (control bit: 0H, 6H)”.

PD6708

<3> Acknowledge bit at the end of a message length field

When either of the following conditions is met, the acknowledge bit at the end of the message length field is NAK,

and communication is discontinued.

• If the parity of the message length bits is incorrect.

• If a timing error occurs.

<4> Acknowledge bit at the end of a data field

When any of the following conditions is met, the acknowledge bit at the end of a data field is NAK, and communication

is discontinued.

• If the parity of the data bits is incorrect

• If a timing error occurred in or after the previous acknowledge bit transmission.

• If the receive buffer is full and cannot accept any more data

Note In this case, if the number of transfer bytes is within the maximum number of bytes which can be transmitted, the

transmitting side re-executes transmission of that data field.

Note

2.4 Transfer Data (Contents of Data Field)

The contents of the data field are data specified by the control bits.

Table 2-3. Functions of Control Bits

PD6708

Note 1

★

Bit 3 0H 0 0 0 0 Reads slave status (SSR) 1H 0 0 0 1 Undefined 2H 0 0 1 0 Undefined 3H 0 0 1 1 Reads and locks data 4H 0 1 0 0 Reads lock address (lower 8 bits) 5H 0 1 0 1 Reads lock address (higher 4 bits) 6H 0 1 1 0 Reads and unlocks slave status (SSR) 7H 0 1 1 1 Reads data 8H 1 0 0 0 Undefined 9H 1 0 0 1 Undefined AH 1 0 1 0 Writes and locks command BH 1 0 1 1 Writes and locks data CH 1 1 0 0 Undefined DH 1 1 0 1 Undefined EH 1 1 1 0 Writes command FH 1 1 1 1 Writes data

Bit 2 Bit 1 Bit 0 Function

Note 2

Notes 1. Depending on the value of bit 3 (MSB), the transfer direction of the message length bits of the subsequent

message field and data field differs. When bit 3 is “1”, data are transferred from the master unit to the slave unit. When bit 3 is “1”, data are transferred from the slave unit to the master unit.

2. 3H, 6H, AH, and BH are control bits that specify locking or unlocking. If any of undefined values 1H, 2H, 8H, 9H, CH, or DH is transmitted, no acknowledge bit is returned.

A unit locked by the master unit rejects acknowledging the control bits and does not output the acknowledge bit if the

control bits received from the master unit which requested locking is in any other state than that shown in Table 2-4.

Table 2-4. Control Field Corresponding to Locked Slave Unit

Bit 3 Bit 2 Bit 1 Bit 0 Function

0H 0 0 0 0 Reads slave status 4H 0 1 0 0 Reads lock address (lower 8 bits) 5H 0 1 0 1 Reads lock address (higher 4 bits)

PD6708

(1) Reading slave status (SSR) (control bit: 0H, 6H)

The master unit can learn the reason why the slave unit has not returned the acknowledge bit (ACK) by reading the

slave status.

The slave status is determined by the results of the last communication performed by the slave unit. All the slave units can provide slave status information. The meanings of the slave status are shown in Table 2-5.

Figure 2-2. Bit Configuration of Slave Status (SSR)

MSB LSB

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

Table 2-5. Meanings of Slave Status

Bit Value Meaning

Note 1

Bit 0

Note 2

Bit 1

Bit 2 0 Unit is not locked.

Bit 3 0 Fixed to ‘0’

Note 3

Bit 4

Bit 5 0 Fixed to ‘0’

0 Slave transmit buffer empty 1 Slave transmit buffer is not empty. 0 Slave receive buffer empty 1 Slave receive buffer is not empty.

1 Unit is locked.

0 Slave transmission ends 1 Slave transmission enabled

★

Bit 7 00 Mode 0 Indicates the highest mode the unit Bit 6 01 Mode 1 supports

10 Mode 2 11 For future expansion

Note 4

Notes 1. The slave transmit buffer is the buffer accessed during data read processing (control bits: 3H, 7H).

With the

PD6708, this buffer corresponds to the write data buffer (WDB) when the SETSD command is valid

(see 5.2.6 “SETSD command”).

2. The slave receive buffer is the buffer accessed during data write processing (control bits: 8H, AH, BH, EH, FH). With the

PD6708, this buffer corresponds to the read data buffer (RDB).

3. The value of bit 4 can be selected by INIT command (see 5.2.1 “INIT command”).

4. Because the µPD6708 can support mode 2, bits 7 and 6 are fixed at ‘10’.

PD6708

(2) Transferring data command (control bit: read (3H, 7H), write (AH, BH, EH, FH))

During data read (3H, 7H), the data in the data buffer of the slave unit are read to the master unit. During data write (BH, FH) or during command write (AH, EH), the data the slave unit has received are processed

according to the operation convention.

Remarks 1. The user can voluntarily select data and command as his system requires.

2. Control bits 3H, AH, and BH may be locked depending on the communication condition and status.

(3) Reading lock address (control bits: 4H, 5H)

★

When the lock address is read processing (4H, 5H), the address (12 bits) of the master unit that has issued the lock

instruction is read in 1-byte units, as shown below.

Figure 2-3. Lock Address Configuration

MSB LSB

Control Bits : 4H

Control Bits : 5H

(4) Locking and unlocking (locking (3H, AH, BH), unlocking (6H))

The lock function is used to transfer a message over two or more frames. A locked unit receives data only from the unit that has locked the unit. Locking and unlocking are performed as described below.

<1> Locking

After the transmission/reception of the acknowledge bit ‘0’ of the message length field by the control bits (3H, AH, BH) which specify the lock has ended, if the communication frame is completed without completing the transmission or reception of the number of data bytes specified by the message length bits, the slave unit is locked by the master unit. At this time, the bit (bit 2) relating to the locking of the byte which indicates the slave status is set to ‘1’.

<2> Unlocking

After completion of transmission or reception of data in one frame by the number of data bytes specified by the message length bits with control bits (3H, AH, or BH) specifying locking or control bits (6H) specifying unlocking, the slave unit is unlocked by the master unit. At this time, the bit (bit 2) relating to the locking of the byte which indicates the slave status is reset to ‘0’.

Lower 8 Bits

Undefined Higher 4 Bits

Locking and unlocking are not performed in the case of broadcast communication.

Caution To unlock the unit specified to be unlocked by the unit itself, the INIT command (see 5.2.1 “INIT

command”) must be executed with the the GETSA command (see 5.2.7 “GETSA command”).

PD6708 (Whether a unit is locked or not can be checked by using

2.5 Bit Format

The IEBus communication frame bit format (concept) is shown in Figure 2-4.

Figure 2-4. IEBus Bit Format (Concept)

Logic "1"

Logic "0"

PD6708

★

Preparation Period

Logic “1”: Potential difference between bus lines (BUS+ pin and BUS– pin) is 20 mV or lower (low level). Logic “0”: Potential difference between bus lines (BUS+ pin and BUS– pin) is 120 mV or higher (high level).

Preparation period: The first or subsequent low-level (logic “1”) period Synchronous period: The next high-level (logic “0”) period Data period: The period that expresses the bit value (logic “1”: low level; logic “0”: high level)

The synchronous period and data period have approximately the same length.

The IEBus uses bit-by-bit synchronization. The specifications for the total bit time and the periods allocated to the bits

depend on the type of transfer bit, and on whether the unit is the master unit or the slave unit.

Synchronous Period

Data Period

Preparation Period

Synchronous Period

Data Period

3. INTERNAL CONFIGURATION

The µPD6708 is composed of the following four blocks.

(1) Data link layer controller (2) Physical layer controller (3) IEBus driver/receiver (4) Host interface

Figure 3-1. µPD6708 Internal Blocks

Status Register

(STR)

Host Interface

PD6708

BUS+

BUS–

IEBus Driver/Receiver

Receiver

Driver

Data Link Layer Controller

Filter

Bit Sequencer

Physical Layer Controller

Read Data Buffer

(RDB) 20 Bytes

Write Data Buffer

(WDB) 4 Bytes

Command Register

(CMR)

Shift

Serial I/O Controller

SCK

CS IRQ C/D R/W

PD6708

3.1 Data Link Layer Controller

The data link layer controller performs processing of the IEBus protocol data link layer (frame composition and resolution,

communication error detection, etc.), execution of communication control commands set by the host controller, and generate a return code that informs the host controller of the communication status.

3.2 Physical Layer Controller

The physical controller performs generation and resolution of bit timing and also converts the signals between the bus

lines through the driver/receiver.

3.3 IEBus Driver/Receiver

The driver/receiver performs conversion between the logic signals within the µPD6708 and the IEBus signals. The IEBus

signals and their relationship to the logic statuses are shown in Table 3-1.

Table 3-1. Relationship between IEBus Signals and Logical Statuses

Logical Status IEBus Signals

0 (BUS+) – (BUS–) ≥ 120mV 1 (BUS+) – (BUS–) ≤ 20mV

3.4 Host Interface

The host Interface is a block which controls the transmission and reception of data to and from the host controller. It

accepts communication control commands, passes on return codes, and forwards transmit data.

The forwarding of transmit data takes place through the FIFO buffers, 4 bytes of write data buffer (WDB) and 20 bytes

of read data buffer (RDB). It also absorbs the differences between IEBus transmission speed and the transmission speed on the serial interface between the

PD6708 and the host controller.

PD6708

4. INTERFACING WITH HOST CONTROLLER

This chapter will explain the interfacing that occurs between the µPD6708 and the host controller.

4.1 Accessible Buffers and Registers from Host Controller

The host controller, which controls the µPD6708, can access the write data (WDB), the read data buffer (RDB), the

command register (CMR), and the status register (STR) within the

4.1.1 Write data buffer (WDB)

WDB is a 4-byte FIFO buffer in which the host controller transmit data and the parameters of the communication control

commands are written.

4.1.2 Read data buffer (RDB)

RDB is a 20-byte FIFO buffer which stores the receive data acknowledged by the data link layer controller in the

The host controller reads the

PD6708 receive data from RDB.

4.1.3 Command register (CMR)

CMR is an 8-bit register used to write control commands for the µPD6708. As shown in Table 4-1, the host controller sets the reset mode and the host interface mode in higher 4 bits and sets the

communication control command code in lower 4 bits.

PD6708.

Table 4-1. Contents of Command Register

Bit Value Meaning

Bit 7 1 Entering the reset mode

0 Exiting the reset mode

Bit 6 1 Data of lower 4 bits of CMR is valid.

0 Data of lower 4 bits of CMR is not valid. Bit 5 00 Change of mode through pin control Switches the host interface mode Bit 4 01 Data write mode

10 Data read mode 11 Status read mode

Bit 3 to Set the communication control command codes Bit 0

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