MAX3140 Datasheet, PDF (1/36 Pages) Maxim Integrated Products – SPI/MICROWIRE-Compatible UART with Integrated True Fail-Safe RS-485/RS-422 Transceivers

19-1453; Rev 0; 6/99
SPI/MICROWIRE-Compatible UART with Integrated
True Fail-Safe RS-485/RS-422 Transceivers
General Description
The MAX3140 is a complete universal asynchronous
receiver-transmitter (UART) and a true fail-safe RS-
485/RS-422 transceiver combined in a single 28-pin
QSOP package for space-, cost-, and power-con-
strained applications. The MAX3140 saves additional
board space as well as microcontroller (µC) I/O pins by
featuring an SPI™/QSPI™/MICROWIRE™-compatible
serial interface. It is pin-programmable for configuration
in all RS-485/RS-422 networks.
The MAX3140 includes a single RS-485/RS-422 driver
and receiver featuring true fail-safe circuitry, which
guarantees a logic-high receiver output when the
receiver inputs are open or shorted. This feature pro-
vides immunity to faults without requiring complex ter-
mination. The MAX3140 provides software-selectable
control of half- or full-duplex operation, data rate, slew
rate, and transmitter and receiver phase. The RS-485
driver slew rate is programmable to minimize EMI and
results in maximum data rates of 115kbps, 500kbps,
and 10Mbps. Independent transmitter/receiver phase
control enables software correction of twisted-pair
polarity reversal. A 1/8-unit-load receiver input imped-
ance allows up to 256 transceivers on the bus.
The MAX3140’s UART includes an oscillator circuit
derived from an external crystal, and a baud-rate gen-
erator with software-programmable divider ratios for all
common baud rates from 300 baud to 230k baud. The
UART features an 8-word-deep receive FIFO that mini-
mizes processor overhead and provides a flexible inter-
rupt with four maskable sources, including address
recognition on 9-bit networks. Two control lines are
included for hardware handshaking—one input and
one output.
The MAX3140 operates from a single +5V supply and
typically consumes only 645µA with the receiver active.
Hardware-invoked shutdown reduces supply current to
only 20µA. The UART and RS-485/RS-422 functions can
be used together or independently since the two func-
tions share only supply and ground connections (the
MAX3140 is hardware- and software-compatible with the
MAX3100 and MAX3089).
Applications
Industrial-Control
Local Area Networks
Transceivers for EMI-
Sensitive Applications
HVAC and Building Control Embedded Systems
Point-of-Sale Devices
Intelligent Instrumentation
Features
o Integrated UART and RS-485/RS-422 Transceiver
in a Single 28-Pin QSOP
o SPI/MICROWIRE-Compatible Interface Saves µC
I/O Pins
o True Fail-Safe Receiver Output Eliminates
Complex Network Termination
o Pin-Programmable RS-485/RS-422 Features
Half/Full-Duplex Operation
Slew-Rate Limiting for Reduced EMI
115kbps/500kbps/10Mbps Data Rates
Receiver/Transmitter Phase for Twisted-Pair
Polarity Reversal
o Full-Featured UART
Programmable Up to 230k baud with a
3.6864MHz Crystal
8-Word Receive FIFO Minimizes Processor
Overhead
9-Bit Address-Recognition Interrupt
o Allows Up to 256 Transceivers on the Bus
o Low 20µA Hardware Shutdown Mode
o Hardware/Software-Compatible with MAX3100
and MAX3089
PART
MAX3140CEI
MAX3140EEI
Ordering Information
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
28 QSOP
28 QSOP
Typical Application Circuit
MAX3140
SPI/
MICRO-
WIRE
CS
CONTROL
LOGIC
RS-485
RS-422
R_t
SCLK
µP
DIN
DOUT
UART
IRQ
R_t
SPI/QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
Pin Configuration appears at end of data sheet.
H/F SRLTXP RXP
HALF/FULL-DUPLEX
RS-485/RS-422
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