Maxim MAX3100EPD, MAX3100EEE, MAX3100CPD Datasheet

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_______________General Description

The MAX3100 universal asynchronous receiver transmit­ter (UART) is the first UART specifically optimized for
small microcontroller-based systems. Using an
SPI™/Microwire™ interface for communication with the
host microcontroller (µC), the MAX3100 comes in a com­pact 16-pin QSOP. The asynchronous I/O is suitable for
use in RS-232, RS-485, IR, and opto-isolated data links.
IR-link communication is easy with the MAX3100’s
infrared data association (IrDA) timing mode.

The MAX3100 includes a crystal oscillator and a baud­rate generator with software-programmable divider ratios
for all common baud rates from 300 baud to 230k baud.
A software- or hardware-invoked shutdown lowers quies­cent current to 10µA, while allowing the MAX3100 to
detect receiver activity.

An 8-word-deep first-in/first-out (FIFO) buffer minimizes
processor overhead. This device also includes a flexible
interrupt with four maskable sources, including address
recognition on 9-bit networks. Two hardware-handshak­ing control lines are included (one input and one output).

The MAX3100 is available in 14-pin plastic DIP and small,
16-pin QSOP packages in the commercial and extended
temperature ranges.

________________________Applications

Hand-Held Instruments
Intelligent Instrumentation
UART in SPI Systems
Small Networks in HVAC or Building Control
Isolated RS-232/RS-485: Directly Drives Opto-Couplers
Low-Cost IR Data Links for Computers/Peripherals

____________________________Features

♦ 16-Pin QSOP Package (8-pin SO footprint):

Smallest UART Available

♦ Full-Featured UART:

—IrDA SIR Timing Compatible
—8-Word FIFO Minimizes Processor

Overhead at High Data Rates
—Up to 230k Baud with a 3.6864MHz Crystal
—9-Bit Address-Recognition Interrupt
—Receive Activity Interrupt in Shutdown

♦ SPI/Microwire-Compatible µC Interface
♦ Lowest Power:

—150µA Operating Current at 3.3V
—10µA in Shutdown with Receive Interrupt

♦ +2.7V to +5.5V Supply Voltage in Operating Mode
♦ Schmitt-Trigger Inputs for Opto-Couplers
♦ TX and

RTS Outputs Sink 25mA for Opto-Couplers

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

________________________________________________________________

Maxim Integrated Products

1

14
13
12
11
10

9
8

1
2
3
4
5
6
7

V

CC

TX
RX
RTSCS

SCLK

DOUT

DIN

TOP VIEW

MAX3100

CTS
X1
X2

GND

SHDN

IRQ

DIP

16
15
14
13
12
11
10

9

1
2
3
4
5
6
7
8

V

CC

TX
RX
RTS
N.C.
CTS
X1
X2

DIN

DOUT

SCLK

CS

N.C.

IRQ

SHDN

GND

MAX3100

QSOP

__________________________________________________________Pin Configurations

19-1259; Rev 0; 7/97

PART

MAX3100CPD
MAX3100CEE 0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

14 Plastic DIP
16 QSOP

______________Ordering Information

Typical Operating Circuit appears at end of data sheet.

SPI is a trademark of Motorola, Inc. Microwire is a trademark of National Semiconductor Corp.

MAX3100EPD
MAX3100EEE -40°C to +85°C

-40°C to +85°C 14 Plastic DIP
16 QSOP

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +2.7V to +5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are measured at 9600 baud at TA= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

VCCto GND ...........................................................................+6V

Input Voltage to GND

(

CS, SHDN, X1, CTS, RX, DIN, SCLK) ....-0.3V to (VCC+ 0.3V)

Output Voltage to GND

(DOUT, RTS, TX, X2) ..............................-0.3V to (V

CC

+ 0.3V)

IRQ...........................................................................-0.3V to 6V

TX, RTS Output Current ....................................................100mA

X2, DOUT, IRQ Short-Circuit Duration

(to V

CC

or GND) .........................................................Indefinite

Continuous Power Dissipation (T

A

= +70°C)

Plastic DIP (derate 10.00mW/°C above +70°C) .......... 800mW

QSOP (derate 8.30mW/°C above +70°C).....................667mW

Operating Temperature Ranges

MAX3100C_ _ ......................................................0°C to +70°C

MAX3100E_ _ ...................................................-40°C to +85°C

Storage Temperature Range............................ -65°C to +160°C

Lead Temperature (soldering, 10sec)............................ +300°C

I

SOURCE

= 25µA, TX only

V

IRQ

= 5.5V

I

SINK

= 4mA

DOUT only, CS = V

CC

Shutdown mode

Active mode

I

SOURCE

= 5mA

V

VCC= 3.3V

VX1= 0V and 5.5V

CONDITIONS

VCC- 0.5

V

OH

Output High Voltage

pF5C

OUT

Output Capacitance

µA±1I

LK

Output Leakage

V0.4V

OL

Output Low Voltage

pF5C

OUT

Output Capacitance

µA±1I

LK

Output Leakage

DOUT, TX, RTS: I

SINK

= 4mA

TX, RTS: I

SINK

= 25mA

V

pF5C

IN

Input Capacitance

V0.3 x V

CC

V

IL

Input Low Voltage

V0.7 x V

CC

V

IH

Input High Voltage

0.4

V

OL

Output Low Voltage

0.9

VX1= 0V and 5.5V

VV

CC

/ 2 0.2 x V

CC

V

IL

Input Low Voltage

V0.7 x VCCV

CC

/ 2V

IH

Input High Voltage

V0.05 x V

CC

V

HYST

Input Hysteresis

µA±1I

IL

Input Leakage

pF5C

IN

Input Capacitance

UNITSMIN TYP MAXSYMBOLPARAMETER

2

I

IN

Input Current µA

25

VCC- 0.5

mA

0.27 1

I

CC

VCCSupply Current in
Normal Mode

SHDN bit = 1 or SHDN = 0,
logic inputs are at 0V or V

CC

µA10I

CC

VCCSupply Current in
Shutdown

With 1.8432MHz crystal;
all other logic inputs are at
0V or V

CC

VCC= 5V
VCC= 3.3V 0.15 0.4

V2.7 5.5V

CC

Supply Voltage

LOGIC INPUTS (DIN, SCLK, CS, SHDN, CTS, RX)

OSCILLATOR INPUT (X1)

OUTPUTS (DOUT, TX, RTS)

IRQ OUTPUT (Open Drain)

POWER REQUIREMENTS

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +2.7V to +5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

C

LOAD

= 100pF

C

LOAD

= 100pF, RCS= 10kΩ

C

LOAD

= 100pF

CONDITIONS

ns100t

CL

SCLK Low Time

ns100t

CH

SCLK High Time

ns238t

CP

SCLK Period

ns0t

DH

DIN to SCLK Hold Time

ns100t

DS

DIN to SCLK Setup Time

ns100t

DO

SCLK Fall to DOUT Valid

ns0t

CSH

CS to SCLK Hold Time

ns100t

CSS

CS to SCLK Setup Time

ns100t

TR

CS High to DOUT Tri-State

ns100t

DV

CS Low to DOUT Valid

UNITSMIN TYP MAXSYMBOLPARAMETER

TX, RTS, DOUT: C

LOAD

= 100pF

(Note 1)

ns10t

r

Output Rise Time

ns200t

CSW

CS High Pulse Width

ns100t

CS0

SCLK Rising Edge
to CS Falling

(Note 1) ns200t

CS1

CS Rising Edge
to SCLK Rising

Figure 1. Detailed Serial-Interface Timing

TX, RTS, DOUT, IRQ: C

LOAD

= 100pF

ns10t

f

Output Fall Time

AC TIMING (Figure 1)

Note 1: t

CS0

and t

CS1

specify the minimum separation between SCLK rising edges used to write to other devices on the SPI bus

and the CS used to select the MAX3100. A separation greater than t

CS0

and t

CS1

ensures that the SCLK edge is ignored.

CS

t

CSS

t

DS

t

DH

t

DV

SCLK

DIN

DOUT

t

CSH

• • •

t

t

CL

CH

• • •

• • •

t

DO

• • •

t

CSH

t

TR

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

4 _______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

1000

900

0

-40 -20 40 60 100

SUPPLY CURRENT vs. TEMPERATURE

200
100

800
700

MAX3100-01

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

0 20 80

600
500

400
300

VCC = 3.3V

VCC = 5V

1.8432MHz CRYSTAL
TRANSMITTING AT

115.2 kbps

10

9

0

-40 -20 40 60 100

SHUTDOWN CURRENT

vs. TEMPERATURE

2
1

8
7

MAX3100-02

TEMPERATURE (°C)

SHUTDOWN CURRENT (µA)

0 20 80

6
5

4
3

VCC = 5V

VCC = 3.3V

1.8432MHz CRYSTAL

700

600

0

0 1 3

4

5

SUPPLY CURRENT vs.

EXTERNAL CLOCK FREQUENCY

100

500

MAX3100-03

EXTERNAL CLOCK FREQUENCY (MHz)

SUPPLY CURRENT (µA)

2

400

300

200

V

CC

= 5V

V

CC

= 3.3V

70
60

0

0 0.20.1 0.6 0.7

0.8

1.0

TX, RTS, DOUT OUTPUT CURRENT

vs. OUTPUT LOW VOLTAGE (V

CC

= 3.3V)

10

50

MAX3100-04

VOLTAGE (V)

OUTPUT SINK CURRENT (mA)

0.3 0.50.4 0.9

40

30

20

RTS

TX

DOUT

400

50

100 10k

1000

100k 1M

SUPPLY CURRENT vs. BAUD RATE

150

100

MAX3100-03a

BAUD RATE (bps)

SUPPLY CURRENT (µA)

200

250

350

300

5V
TRANSMITTING

1.8432 MHz
CRYSTAL

3V
TRANSMITTING

5V
STANDBY

3V
STANDBY

90
80

0

0 0.20.1 0.6 0.7

0.8

1.0

TX, RTS, DOUT OUTPUT CURRENT

vs. OUTPUT LOW VOLTAGE (V

CC

= 5V)

10

70

MAX3100-05

VOLTAGE (V)

OUTPUT SINK CURRENT (mA)

0.3 0.50.4 0.9

60
50

40
30
20

RTS

TX

DOUT

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

_______________________________________________________________________________________ 5

______________________________________________________________Pin Description

Crystal Connection. X1 also serves as an external clock input. See

Crystal-Oscillator

Operation—X1, X2 Connection

section.

910

General-Purpose Active-Low Input. Read via the CTS register bit; often used for RS-232 clear­to-send input (Table 1).

1011

General-Purpose Active-Low Output. Controlled by the RTS register bit. Often used for
RS-232 request-to-send output or RS-485 driver enable.

1113

Asynchronous Serial-Data (receiver) Input. The serial information received from the modem or
RS-232/RS-485 receiver. A transition on RX while in shutdown generates an interrupt (Table 5).

1214

Asynchronous Serial-Data (transmitter) Output1315

Active-Low Interrupt Output. Open-drain interrupt output to microprocessor.56
Hardware-Shutdown Input. When shut down (SHDN = 0), the oscillator turns off immediately

without waiting for the current transmission to end, reducing supply current to just leakage
currents.

67

Ground78
Crystal Connection. Leave X2 unconnected for external clock. See

Crystal-Oscillator

Operation—X1, X2 Connection

section.

89

Active-Low Chip-Select Input. DOUT goes high impedance when CS is high. IRQ, TX, and RTS
are always active. Schmitt-trigger input.

44

SPI/Microwire Serial-Clock Input. Schmitt-trigger input.33

SPI/Microwire Serial-Data Output. High impedance when CS is high.

22

SPI/Microwire Serial-Data Input. Schmitt-trigger input.11

X1

CTS

RTS

RX

TX

IRQ

SHDN

GND

X2

CS

SCLK

DOUT

DIN

Positive Supply Pin (2.7V to 5.5V)1416
No Connection. Not internally connected.—5, 12

V

CC

N.C.

PIN

QSOP

FUNCTION

DIP

NAME

_______________Detailed Description

The MAX3100 universal asynchronous receiver trans­mitter (UART) interfaces the SPI/Microwire-compatible,
synchronous serial data from a microprocessor (µP) to
asynchronous, serial-data communication ports (RS­232, RS-485, IrDA). Figure 2 shows the MAX3100 func­tional diagram.

The MAX3100 combines a simple UART and a baud-rate
generator with an SPI interface and an interrupt genera­tor. Configure the UART by writing a 16-bit word to a
write-configuration register, which contains the baud rate,
data-word length, parity enable, and enable of the 8-word
receive first-in/first-out (FIFO). The write configuration
selects between normal UART timing and IrDA timing,
controls shutdown, and contains 4 interrupt mask bits.

Transmit data by writing a 16-bit word to a write-data
register, where the last 7 or 8 bits are actual data to be
transmitted. Also included is the state of the transmitted
parity bit (if enabled). This register controls the state of

the RTS output pin. Received words generate an inter­rupt if the receive-bit interrupt is enabled.

Read data from a 16-bit register that holds the oldest
data from the receive FIFO, the received parity data,
and the logic level at the CTS input pin. This register
also contains a bit that is the framing error in normal
operation and a receive-activity indicator in shutdown.

The baud-rate generator determines the rate at which the
transmitter and receiver operate. Bits B0 to B3 in the
write-configuration register determine the baud-rate divi­sor (BRD), which divides down the X1 oscillator frequen­cy. The baud clock is 16 times the data rate (baud rate).

The transmitter section accepts SPI/Microwire data, for­mats it, and transmits it in asynchronous serial format
from the TX output. Data is loaded into the transmit­buffer register from the SPI/Microwire interface. The
MAX3100 adds start and stop bits to the data and
clocks the data out at the selected baud rate (Table 7).

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

6 _______________________________________________________________________________________

X1

X2

DOUT

BAUD-RATE

GENERATOR

SPI

INTERFACE

BAUD-RATE

GENERATOR

DIN

SCLK

CS

B0

Pt

TX-SHIFT REGISTER

START/STOP-

BIT DETECT

D0t–D7t

RX-SHIFT REGISTER

D0r–D7r

SHDN

FE

RA

XTAL

B1
B2
B3

RX

TX

9

Pt TX-BUFFER REGISTER

9

Pr

RA/FE

(MASKS)

PrRT

RX-BUFFER REGISTER

PrPrRX-BUFFER REGISTER

9

9

I / O

CTS

RTS

IRQ

INTERRUPT

LOGIC

TRANSMIT-DONE (TM)
DATA-RECEIVED (RM)
PARITY (PM)
FRAMING ERROR (RAM)/

RECEIVE ACTIVITY

(SOURCES)

ACTIVITY

DETECT

Figure 2. Functional Diagram

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

_______________________________________________________________________________________ 7

The receiver section receives data in serial form. The
MAX3100 detects a start bit on a high-to-low RX transi­tion (Figure 3). An internal clock samples data at 16
times the data rate. The start bit can occur as much as
one clock cycle before it is detected, as indicated by
the shaded portion. The state of the start bit is defined
as the majority of the 7th, 8th, and 9th sample of the
internal 16x baud clock. Subsequent bits are also
majority sampled. Receive data is stored in an 8-word
FIFO. The FIFO is cleared if it overflows.

The on-board oscillator can use a 1.8432MHz or

3.6864MHz crystal, or it can be driven at X1 with a 45%
to 55% duty-cycle square wave.

SPI Interface

The bit streams for DIN and DOUT consist of 16 bits,
with bits assigned as shown in the

MAX3100

Operations

section. DOUT transitions on SCLK’s falling

edge, and DIN is latched on SCLK’s rising edge (Figure

4). Most operations, such as the clearing of internal
registers, are executed only on CS’s rising edge. The
DIN stream is monitored for its first two bits to tell the
UART the type of data transfer being executed (Write
Config, Read Config, Write Data, Read Data).

Only 16-bit words are expected. If CS goes high in the
middle of a transmission (any time before the 16th bit),
the sequence is aborted (i.e., data does not get written
to individual registers). Every time CS goes low, a new
16-bit stream is expected. An example of a write con­figuration is shown in Figure 4.

1

RX

BAUD

BLOCK

2 3 4 5 6 7 8 9

ONE BAUD PERIOD

10 11

MAJORITY

CENTER

SAMPLER

12 13 14 15 16

A

Figure 3. Start-Bit Timing

1

CS

SCLK

DIN

DOUT

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

DATA

UPDATED

11 FEN SHDN TM RM PM RAM IR ST PE L B3 B2 B1 B0

R T 00 0 0 0 0 0 0 0 0 0 0 0 0

Figure 4. SPI Interface (Write Configuration)

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

8 _______________________________________________________________________________________

MAX3100 Operations

Write Operations

Table 1 shows write-configuration data. A 16-bit
SPI/Microwire write configuration clears the receive
FIFO and the R, T, RA/FE, D0r–D7r, D0t–D7t, Pr, and Pt
registers. RTS and CTS remain unchanged. The new
configuration is valid on CS’s rising edge if the transmit
buffer is empty (T = 1) and transmission is over. If the
latest transmission has not been completed, the regis­ters are updated when the transmission is over (T = 0).

The write-configuration bits (FEN, SHDNi, IR, ST, PE, L,
B3–B0) take effect after the current transmission is
over. The mask bits (TM, RM, PM, RAM) take effect
immediately after the 16th clock’s rising edge at SCLK.

Read Operations

Table 2 shows read-configuration data. This register
reads back the last configuration written to the

MAX3100. The device enters test mode if bit 0 = 1. In
this mode, if CS = 0, the RTS pin acts as the 16x clock
generator’s output. This may be useful for direct baud­rate generation (in this mode, TX and RX are in digital
loopback).

Normally, the write-data register loads the TX-buffer
register. To change the RTS pin’s state without writing
data, set the TE bit. Setting the TE bit high inhibits the
write command (Table 3).

Reading data clears the R bit and interrupt IRQ (Table 4).

Register Functions

Table 5 shows read/write operation and power-on reset
state (POR), and describes each bit used in program­ming the MAX3100. Figure 5 shows parity and word­length control.

14

0
T

6
D6t
D6r

7
D7t
D7r

15 2

DIN 1 D2t

DOUT R D2r

BIT 3

D3t
D3r

0
D0t
D0r

1
D1t
D1r

4
D4t
D4r

5
D5t
D5r

10

TE

RA/FE

11

0
0

8
Pt
Pr

9
RTS
CTS

12

0
0

13

0
0

14

0
T

6
0

D6r

7
0

D7r

15 2

DIN 0 0

DOUT R D2r

BIT 3

0

D3r

0
0

D0r

1
0

D1r

4
0

D4r

5
0

D5r

10

0

RA/FE

11

0
0

8
0

Pr

9

0
CTS

12

0
0

13

0
0

Table 3. Write Data (D15, D14 = 1, 0)

Table 4. Read Data (D15, D14 = 0, 0)

14

1
T

6
0

ST

7
0

IR

15 2

DIN 0 0

DOUT R B2

BIT 3

0

B3

0

TEST

B0

1
0

B1

4
0
L

5
0

PE

10

0

RM

11

0

TM

8
0

RAM

9

0

PM

12

0

SHDNo

13

0

FEN

Table 2. Read Configuration (D15, D14 = 0, 1)

6

ST

0

7

IR

0

2

B2

0

3

B3

0

0

B0

0

1

B1

0

4
L
0

5

PE

0

10

RM

0

11

TM

0

8

RAM

0

9

PM

0

12

SHDNi

0

13

FEN

0

15 14

1
T

DIN 1

DOUT R

BIT

Table 1. Write Configuration (D15, D14 = 1, 1)

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

_______________________________________________________________________________________ 9

POR

STATE

DESCRIPTION

0000
0000

XPr r

Receive-Parity Bit. This bit is the extra bit received if PE = 1. Therefore, PE = 1 results in 9-bit
transmissions (L = 0). If PE = 0, then Pr is set to 0. Pr is stored in the FIFO with the receive
data (see the

Nine-Bit Networks

section).

0
0

IR r Reads the value of the IR bit.

L

READ/
WRITE

w

B0–B3 w Baud-Rate Divisor Select Bits. Sets the baud clock’s value (Table 6).
B0–B3 r Baud-Rate Divisor Select Bits. Reads the 4-bit baud clock value assigned to these registers.

BIT

NAME

Bit for setting the word length of the transmitted or received data. L = 0 results in 8-bit words
(9-bit words if PE = 1), see Figure 5. L = 1 results in 7-bit words (8-bit words if PE = 1).

0

X

L r Reads the value of the L bit.

Pt w

Transmit-Parity Bit. This bit is treated as an extra bit that will be transmitted if PE = 1. To be
useful in 9-bit networks, the MAX3100 does not calculate parity. If PE = 0, then this bit (Pt) is
ignored in transmit mode (see the

Nine-Bit Networks

section).

00000000

0

D0r–D7r r

Eight data bits read from the receive FIFO or the receive register. These will be all 0s when
the receive FIFO or the receive registers are empty. When L = 1, D7r is always 0.

FEN

w

FIFO Enable. Enables the receive FIFO when FEN = 0. When FEN = 1, FIFO is disabled.
0
0

FEN

r

FIFO-Enable Readback. FEN’s state is read.

IR w Enables the IrDA timing mode when IR = 1.

No

change

X

CTS r

Clear-to-Send-Input. Records the state of the CTS pin (CTS bit = 0 implies CTS pin = logic

high).

D0t–D7t w

Transmit-Buffer Register. Eight data bits written into the transmit-buffer register. D7t is ignored

when L = 1.

Table 5. Bit Descriptions

0PE w

Parity-Enable Bit. Appends the Pt bit to the transmitted data when PE = 1, and sends the Pt

bit as written. No parity bit is transmitted when PE = 0. With PE = 1, an extra bit is expected to

be received. This data is put into the Pr register. Pr = 0 when PE = 0. The MAX3100 does not

calculate parity.
0PE r Reads the value of the Parity-Enable bit.

0

PM

w

Mask for Pr bit. IRQ is asserted if PM = 1 and Pr = 1 (Table 6).
0

PM

r

Reads the value of the PM bit (Table 6).
0R r

Receive Bit or FIFO Not Empty Flag. R = 1 means new data is available to be read from the

receive register or FIFO.
0

RM

w

Mask for R bit. IRQ is asserted if RM = 1 and R = 1 (Table 6).
0

RM

r

Reads the value of the RM bit (Table 6).
0

RAM

w

Mask for RA/FE bit. IRQ is asserted if RAM = 1 and RA/FE = 1 (Table 6).
0

RAM

r

Reads the value of the RAM bit (Table 6).
0RTS w

Request-to-Send Bit. Controls the state of the RTS output. This bit is reset on power-up (RTS

bit = 0 sets the RTS pin = logic high).

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

10 ______________________________________________________________________________________

Table 5. Bit Descriptions (continued)

POR

STATE

DESCRIPTION

READ/

WRITE

BIT

NAME

0SHDNi w

Software-Shutdown Bit. Enter software shutdown with a write configuration where SHDNi = 1.

Software shutdown takes effect after CS goes high, and causes the oscillator to stop as soon

as the transmitter becomes idle. Software shutdown also clears R, T, RA/FE, D0r–D7r,

D0t–D7t, Pr, Pt, and all data in the receive FIFO. RTS and CTS can be read and updated

while in shutdown. Exit software shutdown with a write configuration where SHDNi = 0. The

oscillator restarts typically within 50ms of CS going high. RTS and CTS are unaffected. Refer

to the

Pin Description

for hardware shutdown (SHDN input).

0SHDNo r

Shutdown Read-Back Bit. The read-configuration register outputs SHDNo = 1 when the UART

is in shutdown. Note that this bit is not sent until the current byte in the transmitter is sent (T =

1). This tells the processor when it may shut down the RS-232 driver. This bit is also set imme-

diately when the device is shut down through the SHDN pin.

0RA/FE r

Receiver-Activity/Framing-Error Bit. In shutdown mode, this is the RA bit. In normal operation,

this is the FE bit. In shutdown mode, a transition on RX sets RA = 1. In normal mode, a fram-

ing error sets FE = 1. A framing error occurs if a zero is received when the first stop bit is

expected. FE is set when a framing error occurs, and cleared upon receipt of the next proper-

ly framed character independent of the FIFO being enabled. When the device wakes up, it is

likely that a framing error will occur. This error can be cleared with a write configuration. The

FE bit is not cleared on a Read Data operation. When an FE is encountered, the UART resets

itself to the state where it is looking for a start bit.

0ST w

Transmit-Stop Bit. One stop bit will be transmitted when ST = 0. Two stop bits will be transmit-

ted when ST = 1. The receiver only requires one stop bit.
0ST r Reads the value of the ST bit.

0

TM

w

Mask for T bit. IRQ is asserted if TM = 1 and T = 1 (Table 6).
0

TM

r

Reads the value of the TM bit (Table 6).

1T r

Transmit-Buffer-Empty Flag. T = 1 means that the transmit buffer is empty and ready to

accept another data word.

0

TE

w

Transmit-Enable Bit. If TE = 1, then only the RTS pin will be updated on CS’s rising edge. The

contents of RTS, Pt, and D0t–D7t transmit on CS’s rising edge when TE = 0.

Figure 5. Parity and Word-Length Control

PE = 0, L = 0

IDLE

IDLE

IDLE

IDLE
TIME

D0START D1 D2 D3 D4 D5 D6 D7 STOP STOP IDLE

PE = 0, L = 1

D0START D1 D2 D3 D4 D5 D6 STOP STOP IDLE

PE = 1, L = 0

D0START D1 D2 D3 D4 D5 D6 D7 Pt STOP STOP IDLE

PE = 1, L = 1

D0START D1 D2 D3 D4 D5 D6 Pt

SECOND STOP BIT IS OMITTED IF ST = 0.

STOPSTOP

IDLE

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 11

IRQ

N

RM MASK

TM MASK

PM MASK
TRANSITION ON RX

SHUTDOWN

RAM MASK
FRAMING ERROR

SHUTDOWN

RAM MASK

R

S

Q

R

NEW DATA AVAILABLE
DATA READ

TRANSMIT BUFFER EMPTY
DATA READ

PE = 1 AND RECEIVED PARITY BIT = 1
PE = 0 OR RECEIVED PARITY BIT = 0

T

Pr

RA

FE

R

S

Q

R

S

Q

Figure 6. Interrupt Sources and Masks Functional Diagram

Table 6. Interrupt Sources and Masks—Bit Descriptions

MEANING

WHEN SET

DESCRIPTION

Received parity bit = 1

Transition on RX when
in shutdown; framing
error when not in
shutdown

RA/FE

RAM

This is the RA (RX-transition) bit in shutdown, and the FE (framing-error) bit in
operating mode. RA is set if there has been a transition on RX since entering
shutdown. RA is cleared when the MAX3100 exits shutdown. IRQ is asserted
when RA is set and RAM = 1.

FE is determined solely by the currently received data, and is not stored in FIFO.
The FE bit is set if a zero is received when the first stop bit is expected. FE is
cleared upon receipt of the next properly framed character. IRQ is asserted
when FE is set and RAM = 1.

MASK

BIT

Pr

PM

The Pr bit reflects the value in the word currently in the receive-buffer register
(oldest data available). The Pr bit is set when parity is enabled (PE = 1) and the
received parity bit is 1. The Pr bit is cleared either when parity is not enabled (PE
= 0), or when parity is enabled and the received bit is 0. An interrupt is issued
based on the oldest Pr value in the receiver FIFO. The oldest Pr value is the next
value that will be read by a Read Data operation.

BIT

NAME

Data availableR

RM

The R bit is set when new data is available to be read from the receive register/
FIFO. FIFO is cleared when all data has been read. An interrupt is asserted as long
as R = 1 and RM = 1.

Transmit buffer is
empty

T

TM

The T bit is set when the transmit buffer is ready to accept data. IRQ is asserted
low if TM = 1 and the transmit buffer becomes empty. This source is cleared on
CS’s rising edge during a Read Data operation. Although the interrupt is cleared,
T may be polled to determine transmit-buffer status.

Interrupt Sources and Masks

A Read Data operation clears the interrupt IRQ. Table
6 gives the details for each interrupt source. Figure 6

shows the functional diagram for the interrupt sources
and mask blocks.

Clock-Oscillator Baud Rates

Bits B0–B3 of the write-configuration register determine
the baud rate. Table 7 shows baud-rate divisors for given
input codes, as well as the given baud rate for

1.8432MHz and 3.6864MHz crystals. Note that the baud
rate = crystal frequency / 16x division ratio.

Shutdown Mode

In shutdown, the oscillator turns off to reduce power
dissipation (ICC< 10µA). The MAX3100 enters shut­down in one of two ways: by a software command
(SHDNi bit = 1) or by a hardware command (SHDN =
logic low). The hardware shutdown is effective immedi­ately and will immediately terminate any transmission in
progress. The software shutdown, requested by setting
SHDNi bit = 1, is entered upon completing the trans­mission of the data in both the transmit register and the
transmit-buffer register. The SHDNo bit is set when the
MAX3100 enters shutdown (either hardware or soft­ware). The microcontroller (µC) can monitor the SHDNo
bit to determine when all data has been transmitted,
and shut down any external circuitry (such as RS-232
transceivers) at that time.

Shutdown clears the receive FIFO, R, A, RA/FE,
D0r–D7r, Pr, and Pt registers and sets the T bit high.
Configuration bits (RM, TM, PM, RAM, IR, ST, PE, L,
B0-3, and RTS) can be modified when SHDNo = 1 and
CTS can also be read. Even though RA is reset upon
entering shutdown, it will go high when any transitions
are detected on the RX pin. This allows the UART to
monitor activity on the receiver when in shutdown.

The command to power up (SHDNi = 0) turns on the
oscillator when CS goes high if SHDN pin = logic high,
with a start-up time of about 25ms. This is done through
a write configuration, which clears all registers but RTS
and CTS. Since the crystal oscillator typically requires
25ms to start, the first received characters will be gar­bled, and a framing error may occur.

__________Applications Information

Driving Opto-Couplers

Figure 7 shows the MAX3100 in an isolated serial inter­face. The MAX3100 Schmitt-trigger inputs are driven
directly by opto-coupler outputs. Isolated power is pro­vided by the MAX845 transformer driver and linear reg­ulator shown. A significant feature of this application is
that the opto-coupler’s skew does not affect the asyn­chronous serial output’s timing. Only the set-up and
hold times of the SPI interface need to be met.

Figure 8 shows a bidirectional opto-isolated interface
using only two opto-isolators. Over 81% power savings
is realized using IrDA mode due to its 3/16-wide baud
periods.

Crystal-Oscillator Operation—

X1, X2 Connection

The MAX3100 includes a crystal oscillator for baud-rate
generation. For standard baud rates, use a 1.8432MHz
or 3.6864MHz crystal. The 1.8432MHz crystal results in
lower operating current; however, the 3.6864MHz crys­tal may be more readily available in surface mount.

Ceramic resonators are low-cost alternatives to crystals
and operate similarly, though the “Q” and accuracy are
lower. Some ceramic resonators are available with inte­gral load capacitors, which can further reduce cost.
The tradeoff between crystals and ceramic resonators
is in initial frequency accuracy and temperature drift.
The total error in the baud-rate generator should be
kept below 1% for reliable operation with other sys­tems. This is accomplished easily with a crystal, and in
most cases can be achieved with ceramic resonators.
Table 8 lists the different types of crystals and res­onators and their suppliers.

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

12 ______________________________________________________________________________________

Table 7. Baud-Rate Selection Table*

*Standard baud rates shown in bold
**Default baud rate

115.2k

230.4k**

BAUD
RATE

(f

OSC

=

3.6864MHz)

BAUD

B3 B2 B1 B0

20 0 0 1

10 0 0 0**

DIVISION

RATIO

57.6k

115.2k**

BAUD

RATE

(f

OSC

=

1.8432MHz)

28.8k

57.6k

80 0 1 1

40 0 1 0

14.4k

28.8k

7200

14.4k

1800

3600

1280 1 1 1

640 1 1 0

900

1800

320 1 0 1

160 1 0 0

3600

7200

38.4k

76.8k

9600

19.2k

241 0 1 1

121 0 1 0

4800

9600

2400

4800

600

1200

3841 1 1 1

1921 1 1 0

300

600

961 1 0 1

481 1 0 0

1200

2400

61 0 0 1

31 0 0 0

19.2k

38.4k

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 13

MAX3100

MAX3222

CS

ISO
5V

SCLK

ISO

+5V

TX

DIN

2k

6N136

6N136

6N136

6N136

2k

2k

2k

DOUT

CS

SCLK

DIN

DOUT

ISO
+5V

V

CC

V

CC

+5V

MBR0520

HALO

TGM-010P3

V

CC

V

CC

470Ω

RX

CTS

RTS

MAX253

MAX667

470Ω

470Ω

470Ω

LINEAR

REGULATOR

TRANSFORMER

DRIVER

Figure 7. Driving Optocouplers

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

14 ______________________________________________________________________________________

MAX3100

CS
SCLK
DIN
DOUT

TX

RX

+5V

ISO +5V

+5V

V

CC

GND

MAX3100

CS

SCLK

DIN

DOUT

RX

470Ω

470Ω

2k

2k

TX

V

CC

GND

Figure 8. Bidirectional Opto-Isolated Interface

Table 8. Component and Supplier List

This oscillator supports parallel-resonant mode crystals
and ceramic resonators, or can be driven from an
external clock source. Internally, the oscillator consists
of an inverting amplifier with its input, X1, tied to its out­put, X2, by a bias network that self-biases the inverter
at approximately V

CC

/ 2. The external feedback circuit,
usually a crystal, from X2 to X1 provides 180° of phase
shift, causing the circuit to oscillate. As shown in the
standard application circuit, the crystal or resonator is
connected between X1 and X2, with the load capaci­tance for the crystal being the series combination of C1
and C2. For example, a 1.8432MHz crystal with a spec-

ified load capacitance of 11pF would use capacitors of
22pF on either side of the crystal to ground. Series-res­onant mode crystals have a slight frequency error, typi­cally oscillating 0.03% higher than specified series­resonant frequency, when operated in parallel mode.

It is very important to keep crystal, resonator, and
load-capacitor leads and traces as short and direct as
possible. The X1 and X2 trace lengths and ground
tracks should be tight, with no other intervening traces.
This helps minimize parasitic capacitance and noise
pickup in the oscillator, and reduces EMI. Minimize
capacitive loading on X2 to minimize supply current.

Murata North America

ECS International, Inc.

SUPPLIER

CSA1.84MG

ECS-18-13-1

PART

NUMBER

[phone]

[phone]

PHONE

NUMBER

DESCRIPTION

1.8432

Through-Hole
Resonator

1.8432

Through-Hole Crystal
(HC-49/U)

FREQUENCY

(MHz)

47

25

TYPICAL

C1, C2 (pF)

ECS International, Inc.

ECS International, Inc.

ECS-36-20-5P

ECS-36-18-4

[phone]

[phone]

3.6864SMT Crystal

3.6864

Through-Hole Crystal
(HC-49/US)

39

33

AVX/Kyocera PBRC-3.68B [phone]3.6864SMT Resonator

None

(integral)

The MAX3100 X1 input can be driven directly by an
external CMOS clock source. The trip level is approxi­mately equal to V

CC

/ 2. No connection should be
made to X2 in this mode. If a TTL or non-CMOS clock
source is used, AC couple with a 10nF capacitor to X1.
The peak-to-peak swing on the input should be at least
2V for reliable operation.

9-Bit Networks

The MAX3100 supports a common multidrop communi­cation technique referred to as 9-bit mode. In this mode,
the parity bit is set to indicate a message that contains a
header with a destination address. The MAX3100 parity
mask can be set to generate interrupts for this condition.
Operating a network in this mode reduces the process­ing overhead of all nodes by enabling the slave con­trollers to ignore most message traffic. This can relieve
the remote processor to handle more useful tasks.

In 9-bit mode, the MAX3100 is set up with 8 bits plus
parity. The parity bit in all normal messages is clear, but
is set in an address-type message. The MAX3100 pari­ty-interrupt mask is enabled to generate an interrupt on
high parity. When the master sends an address mes­sage with the parity bit set, all MAX3100 nodes issue an
interrupt. All nodes then retrieve the received byte to
compare to their assigned address. Once addressed,
the node continues to process each received byte. If the
node was not addressed, it ignores all message traffic
until a new address is sent out by the master.

The parity/9th-bit interrupt is controlled only by the data
in the receive register, and is not affected by data in
the FIFO, so the most effective use of the parity/9th-bit
interrupt is with FIFO disabled. With the FIFO disabled,
received nonaddress words can be ignored and not
even read from the UART.

SIR IrDA Mode

The MAX3100’s IrDA mode can be used to communicate
with other IrDA SIR-compatible devices, or to reduce
power consumption in opto-isolated applications.

In IrDA mode, a bit period is shortened to 3/16 of a
baud period (1.6µs at 115,200 baud) (Figure 9). A data
zero is transmitted as a pulse of light (TX pin = logic
low, RX pin = logic high).

In receive mode, the RX signal’s sampling is done
halfway into the transmission of a high level. The sam­pling is done once, instead of three times, as in normal
mode. The MAX3100 ignores pulses shorter than
approximately 1/16 of the baud period. The IrDA device
that is communicating with the MAX3100 must be set to
transmit pulses at 3/16 of the baud period. For compati­bility with other IrDA devices, set the format to 8-bit
data, one stop, no parity.

IrDA Module

The MAX3100 was optimized for direct optocoupler
drive, whereas IrDA modules contain inverting buffers.
Invert the RX and TX outputs as shown in Figure 10.

8051 Example: IrDA to RS-232 Converter

Figure 10 shows the MAX3100 with an 8051 µC. This
circuit receives IrDA data and outputs standard RS-232
data. Although the 8051 contains an internal UART, it
does not support IrDA or high-speed communications.
The MAX3100 can easily interface to the 8051 to sup­port these high-performance communications modes.
The 8051 does not have an SPI interface, so communi­cation with the MAX3100 is accomplished with port
pins and a short software routine (Figure 12a).

The software routine polls the IRQ output to see if data
is available from the MAX3100 UART. It then shifts the
data out, using the 8051 port pins, and transmits it out
the RS-232 side through the MAX3221 driver. The 8051
simultaneously monitors its internal UART for incoming
communications from the RS-232 side, and transmits
this data out the IrDA side through the MAX3100. The
low-level routine (UTLK) is the core routine that sends
and receives data over the port pins to simulate an SPI
port on the 8051. This technique is useful for any 8051­based MAX3100 port-pin-interfaced application.

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 15

START

STOP

START

STOP

NORMAL

RX

UART FRAME

DATA BITS

0 1 1 1 1 10 0 0 0

NORMAL UART

TX

1 1 1 1 10 0 0 0

IrDA

RX

IrDA

TX

Figure 9. IrDA Timing

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

16 ______________________________________________________________________________________

MAX3100 3100

IRQ RX

TX

RX

TX

RXD

TXD

22pF 22pF

330Ω

IR LED

+5V

1/6 HC00

1/6 HC00

DIRECT

OPTO-COUPLER

DRIVE

OR

IR MODULE

DRIVE

IR

MODULE

8051

MAX3221

100Ω

0.1µF

+5V

1.8432MHz

10k

Figure 10. Bidirectional RS-232 IrDA Using an 8051

Interface to PIC Processor

(“Quick Brown Fox” Generator)

Figure 11 illustrates the use of the MAX3100 with the
PIC®. This circuit is a “Quick Brown Fox” generator that
repeatedly transmits “THE QUICK BROWN FOX JUMPS
OVER THE LAZY DOG” (covering the entire alphabet)
over an RS-232 link with adjustable baud rate, word
length, and delay. Although a software-based UART
could be implemented on the PIC, features like accu­rate variable baud rates, high baud rates, and simple
protocol selection would be difficult to implement reli­ably. The 16C54 in the example is the most basic of the
PICs. Thus, it is possible to implement the example on
any member of the PIC family.

The software routine (Figure 12) begins by reading the
DIP switch on port RB. The switch data includes 4 bits
for the baud rate, 1 bit for number of stop bits, 1 bit for
a word length of 7 or 8 bits, and 1 bit for delay between
messages. The PIC reads the switch only at initializa­tion (reset), and programs the parameters into the
MAX3100. It then begins sending the message repeat­edly. If the delay bit is set, it inserts a 1sec delay
between transmissions. As in the 8051 example, the
main routine is called UTLK, and can be used in any
PIC-based, port-pin-interfaced application.

PIC is a registered trademark of Microchip Corporation.

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 17

PIC16C54

V

CC

X1 X2

RB7

RB6

RB5

TX

22pF22pF

RB4

RB3

RB2

RB1

RB0

GO

Y/N 1µs Delay

1/2 STOP BITS TX

7/8 BITS

B3

RA0

RA1

RA2

RA3

DOUT

DIN

SCLK

CS

B2

B1

B0

100k

100k

100k

100k

100k

100k

100k

100k

1. 8432MHz

MAX3100

MAX3221

Figure 11. Quick Brown Fox Generator

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

18 ______________________________________________________________________________________

Table 10. Synchronous Data Output Format (DOUT pin to microprocessor, SPI MISO)

FEN

0

SHDNo

0

PM0RAM

0

TM0RM

0

PE0L

0

B10B0

0

B30B2R

Read
Config

0R

Write
Config

IR

(IrDA)

0

ST

0

0

0

0

0

CTS

T

T

CTSPrPr

0

0

RA/

FE

RA/

FE

D5r

D5r

D4r

D4r

D1r

D1r

D0r

D0r

D3r

D3r

D2rR

Read
Data

D2rR

Write
Data

D7r

D7r

D6r

D6r

T

T

__________MAX3100 Synchronous-to-Asynchronous SPI UART at a Glance

Table 9. Synchronous Data Input Format (DIN pin from microprocessor, SPI MOSI)

0

0

D6t

0

D7t

0

Write
Data

1 D2t

Read
Data

0 0

D3t

0

D0t

0

D1t

0

D4t

0

D5t

0

TE

0

0

0

Pt

0

RTS

0

0

0

0

0

1

1

ST

0

IR

(IrDA)

0

Write
Config

1 B2

Read
Config

0 0

B3

0

Bit Number

B0

TEST

B1

0

L

0

PE

0

RM

0

TM

0

RAM

0

PM

0

SHDNi

0

FEN

0

14 6715 2

Oper-

ation

3 01451011 891213

Bit Number

13 12 9 811 10 5 4 1 03

Oper-

ation

215 7 614

Table 11. Bit Definitions*

Table 13. 1.8432MHz Baud Rates

Table 12. Field Definitions

*

Default setting is clear

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 19

Baud

115.2k

B3...B0

56k0 0 0 1 2

0 0 0 0 1

28k0 0 1 0 4
14k

BRD

0 0 1 1 8

Baud

38.4k

B3...B0

19.2k1 0 0 1 6

1 0 0 0 3

96001 0 1 0 12
4800

BRD

1 0 1 1 24

2400
12001 1 0 1 96

1 1 0 0 48

6001 1 1 0 192
3001 1 1 1 384

7200
36000 1 0 1 32

0 1 0 0 16

18000 1 1 0 64

9000 1 1 1 128

MeaningRegister Field Name

Baud-rate divisor
Transmit dataWrite Data D7t–D0t

Config B3–B0

Received parity bitRead Data Pr
Received dataRead Data D7r–D0r

Parity disabledParity enabledConfig PE

Enable FIFO
buffer

Disable FIFO
buffer

Bit Set (1) Bit Clear (0)

OperateShutdownConfig SHDNi
Disable transmit-

done interrupt

Enable transmit­done interrupt

Disable data­received
interrupt

Enable data­received inter­rupt

Config

RM

Config

TM

Disable parity
interrupt

Enable parity
interrupt

Disable framing­error interrupt

Enable framing­error interrupt

Config

RAM

Standard
timing

Enable IrDA
timing mode

One stop bitTwo stop bitsConfig ST

Config IR

Config

PM

Config

Register

FEN

Bit

Name

Bit Set (1) Bit Clear (0)

Word length =
8 bits

Word length =
7 bits

Config L

Enable normal
operation

Inhibit TX output

Register

Drive RTS out­put pin high

Drive RTS output
pin low

Write

Data

RTS

Write

Data

TE

Transmit
parity = 0

Transmit
parity = 1

Write

Data

Pt

Normal

Data overrun or
framing error

CTS input pin is
high

CTS input pin is
low

Read

Data

CTS

Data buffer is
empty

Data has been
received

UART is busy
transmitting

Transmit buffer
is empty

All T

All R

Bit

Name

Read

Data

RA/FE

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

20 ______________________________________________________________________________________

Figure 12a. 8051 IrDA/RS-232 Code

Figure 12b. MAX3100 Using PIC µC

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 21

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

22 ______________________________________________________________________________________

Figure 12b. MAX3100 Using PIC µC (continued)

___________________________________________________Typical Operating Circuit

RX

CTS

RTS

TXDIN

DOUT

SPI/MICROWIRE

RS-232 I/O

SCLK

CS

C2

C1

MAX3100

IRQ

MAX3223

µC

MAX3100

SPI/Microwire-Compatible

UART in QSOP-16

______________________________________________________________________________________ 23

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

24

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

MAX3100

SPI/Microwire-Compatible
UART in QSOP-16

___________________Chip Information

TRANSISTOR COUNT: 6848
SUBSTRATE CONNECTED TO GND

________________________________________________________Package Information

QSOP.EPS