ALSTOM MAE99-04 8-way isolated serial interface terminal board

ALSTOM MAE99-04 8-way isolated serial interface terminal board

Job Overview

The board is connected to one of the 8-channel connectors of the PMC-Sweet16 PMC module through a cable; The Sweet16 module is installed on the PMC Span carrier board.

Short term system architecture: PMC Span carrier board mounted on PowerPC host, VME backplane; Long term migration to other PMC carrier boards on the PCI backplane.

Function: The RS232 signal on the processor side is optically isolated and converted into on-site bidirectional RS-485/422; Each port is optically isolated from each other and also isolated from the 0V power supply on the processor side.

Each port: fixed RS-485 at the sending end; Add additional protection circuit at the receiving end, compatible with RS232 level for short distances (<10m); Prioritize using RS485 balanced differential to resist interference, and do not recommend using RS232 on-site.

The RS485 link must have a common 0V reference potential between devices.

Hardware details

2.1 Mechanical Structure

PCB size: 262   mm × 72   mm, compatible with Phoenix 72   mm wide DIN rail base.

Wiring terminal: double-layer spring cage terminal; The upper layer is connected to the on-site incoming cable, and the lower layer can be output in parallel to the second DP console to achieve link branching.

Components: The vast majority are SMD surface mount devices, placed on the PCB soldering surface (bottom) and protected by the base shell; LED reverse installation, visible through PCB openings.

Large area grounding plane on the top layer of PCB for electromagnetic shielding; The DC-DC isolated power supply device is arranged on the top surface of the component.

2.2 Port Logic and TXEN Sending Enable

Sweet16 PMC module side uses RS232 hardware handshake: RXD, TXD, RTS, CTS, 0V; The RTS inside the terminal board is directly short circuited back to CTS.

TXEN sends enable monostable circuit (200ms pulse)

Enable RTS in the software, trigger 200ms monostable pulse, and turn on the RS-485 tri state transmission driver.

200ms pulse width is greater than the conventional message length; To send the next message, you must first clear RTS and then reset RTS.

If receiving data, TXEN monostable will be reset directly to accelerate peripheral interaction speed.

In duplex/triplex multi master redundant systems: only units that are in online working state are allowed to set RTS and send messages.

2.3 Power specifications

On site input power supply: 18-36 VDC (nominal 24 VDC)

24V typical current 120 mA, maximum 200 mA.

On chip Level DC-DC: Generate ± 5V from 24V and supply it to the board logic and RS232 interface with Sweet16.

Each serial port channel has independent isolation DC-DC to achieve electrical isolation of each port.

2.4 LED Status Indication (3 LEDs per channel)

Monitor separately: receive RX data, enable TXEN transmission, isolate power supply.

RX-LED off: no communication, connection is normal;

RX-LED short flashing: normal communication activity;

RX-LED is always on: It is highly likely that the RS485 differential lines RXA/RXB are connected incorrectly.

2.5 Reliability

MTBF=10 ⁶/12.19=82035 hours

Connector pins

3.1 On site terminals TB1-TB9

TB1~TB8 correspond to PORT1~PORT8, with double-layer spring cage terminals: upper layer on-site incoming line, lower layer parallel output to the second console. Each port signal: TXA, TXB, 0VI (isolated ground) RXA； TB9 is a 4-channel screw terminal used for 24V power input and can output 24V to the second panel.

3.2 PMC side connector SK1

50 pin SCSI straight female socket, connected to Sweet16 PMC module; Includes TXD, RXD, RTS, CTS, GPI, GND signals with 8 serial ports, and the document provides a complete 50 pin pin allocation table.

Application Description

The attached document provides three typical topologies:

RS-485 bidirectional multi-point (multi station) link (typical of Triplex triple redundancy system)

RS-485 unidirectional link

RS-232 unidirectional link

Cable shielding treatment: Each MAE99-04 device needs to be equipped with a grounding busbar on the on-site side; Cable shielding layer connected to busbar; The busbar is connected to the installation base plate ground through metal pillars.

Attention: A multi master triplet system requires software logic to ensure that only online hosts are allowed to drive bus transmission.