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M77 - Quad RS232/RS422/RS485 UART


The mezzanine card M77 is a quad serial interface M-Module which supports four high-performance UARTs with RS232 or RS422/485.

  • M77 Product ImageM77 Quad RS232/RS422/RS485 UART
  • M77 Product Image

Main Features

  • 4 high-performance UARTs
  • 128 bytes FIFO buffer
  • Serial data rates up to 1.152 Mbit/s
  • Software programmable 
  • Full and half duplex on 4 channels
  • 500 V DC optical isolation
  • 180 V DC isolation between channels
  • -40 to +85°C screened versions
M77 Product Image

Technical Data

Quad RS232/485/422 Interface
  • All 4 channels with 4 lines (no handshake lines)
  • All 4 channels electrically isolated from the system and from each other
UART Controller
  • 4 independent full-duplex asynchronous 16C950 high performance UART channels each
  • 128-byte FIFO for each transmitter and receiver
  • UARTs fully software compatible with industry standard 16C55x type UARTs
  • Data rates up to 1.152 Mbit/s
  • Readable FIFO levels
  • Automated in-band flow control using programmable Xon/Xoff characters, in both directions
  • Arbitrary trigger levels for receiver and transmitter FIFO interrupts
  • Programmable special character detection
  • 5-, 6-, 7-, 8- and 9-bits data framing
  • Detection of bad data in receiver FIFO
  • Independent channel reset by software
  • Transmitter and receiver can be disabled
  • Transmitter idle interrupt
  • Sleep mode (low operating current)
Peripheral Connections
  • Via front panel on a shielded 25-pin D-Sub receptacle connector
  • Via carrier board (rear I/O)
M-Module Characteristics
  • Compliant with M-Module standard
  • A08, D08, INTA, IDENT
Electrical Specifications
  • Isolation voltage:
    • 500V DC between isolated side and digital side
    • 180V DC between the channels
    • Voltage between the connector shield and isolated ground is limited to 180V using a varistor; AC coupling between connector shield and isolated ground through 47nF capacitor
  • Supply voltage/power consumption: +5V (4.85V..5.25V), 200mA typ.
  • MTBF: 272,598h @ 40°C according to IEC/TR 62380 (RDF 2000)
Mechanical Specifications
  • Dimensions: conforming to M-Module Standard
  • Weight: 67g
Environmental Specifications
  • Temperature range (operation):
    • 0..+60°C or -40..+85°C
    • Airflow: min. 10m³/h
  • Temperature range (storage): -40..+85°C
  • Relative humidity range (operation): max. 95% non-condensing
  • Relative humidity range (storage): max. 95% non-condensing
  • Altitude: -300m to + 3,000m
  • Shock: 15g/11ms
  • Bump: 10g/16ms
  • Vibration (sinusoidal): 2g/10..150Hz
  • Conformal coating on request
PCB manufactured with a flammability rating of 94V-0 by UL recognized manufacturers
Tested according to EN 55022 (radio disturbance), IEC1000-4-2 (ESD) and IEC1000-4-4 (burst)
Software Support
  • Linux
  • VxWorks
  • QNX
  • OS-9
  • For more information on supported operating system versions and drivers see Software.

Ordering Information

Standard M77 Models

4-channels RS232/RS485/RS422, optically isolated UART, 0..+60°C


4-channel RS232/RS485/RS422, optically isolated UART, -40..+85°C screened

Miscellaneous Accessories

M-Module cable, 2m, with 25-pin D-Sub plug/housing to pig tail


25 mounting screw sets to fix M-Modules on carrier boards



Linux TTY driver (MEN) for M77, M45N and M69N, source code


VxWorks driver (MEN) for M77, M45N and M69N, source code


QNX native driver (MEN) for M77, M45N and M69N


OS-9/68k SCF driver for M77


OS-9/PPC SCF driver for (MEN) M77, M45N and M69N, source code

Application Examples

Power Automation

3U CompactPCI systems are used as the computing heart of a station master system on the plant control level.