Description
Key Technical Specifications
| Parameter | Value |
|---|---|
| Manufacturer | GE Fanuc |
| Product Family | PACSystems RX7i / Series 90-70 |
| Model | IC687BEM731-AB |
| Product Type | Genius Bus Controller |
| Bus | GE Genius Communications Bus |
| Channels | 1 |
| Genius Devices | Up to 31 additional devices |
| Mounting | Single PLC backplane slot |
| Backplane Type | VME-type / standard-width PLC backplane |
| Backplane Voltage | 5 VDC |
| Backplane Current | 1.3 A |
| Bus Speeds | 153.6 kbaud extended; 153.6 kbaud standard; 38.4 kbaud; 6.8 kbaud |
| Maximum Bus Length | Up to 7,500 ft at 38.4 kbaud, depending on cable |
| Bus Topology | Daisy-chain |
| Bus Cable | Twisted pair + shield or Twinax |
| Electrical Isolation | 2,000 V Hi-Pot; 1,500 V transient common-mode rejection |
| Serial Interface | 1 handheld-monitor port |
| Redundancy | Supported |
| Operating Temperature | 0 to 60°C |
| Installation Locations | RX7i slots 2–17; Series 90-70 slots 2–9 |
| Firmware Revision | 6.0 documented for IC687BEM731-AB |
GE documentation identifies the IC687BEM731 as a single-slot Genius Bus Controller for RX7i and Series 90-70 systems. It provides one Genius communications channel and can communicate with up to 31 additional devices on that bus.
The documented Genius bus rates are configurable up to 153.6 kbaud, with maximum cable distance depending on baud rate and cable construction. At 38.4 kbaud, the specified maximum is 7,500 ft under the applicable cable conditions.
Product Introduction
GE Fanuc IC687BEM731-AB Product Introduction
The GE Fanuc IC687BEM731-AB is a Genius Bus Controller used to connect a GE Series 90-70 or PACSystems RX7i PLC to a Genius communications network. It occupies one PLC backplane slot and supports Genius I/O blocks, remote PLCs, VersaMax Genius interfaces, and other compatible Genius devices.
This module is useful in legacy distributed-I/O architectures where Genius remains the field communication layer. The AB revision is significant: GE’s product information identifies firmware 6.0 with IC687BEM731-AB production hardware, and firmware 5.9 or later is required for RX7i operation.
Application Scenarios & Field Pitfalls
Engineering Pain Point
A Genius network fault can look like an I/O-module failure when the actual problem is at the Bus Controller, termination, cable, or bus configuration level. With an RX7i installation, the is the gateway between the PLC backplane and the Genius network. One bad controller can therefore make a whole group of distributed devices disappear at once.
IC687BEM731-AB
Typical Applications
- Manufacturing — RX7i control systems communicating with distributed Genius I/O blocks.
- Water & Wastewater — Remote pump, valve, and instrumentation I/O distributed over Genius networks.
- Power & Utilities — Legacy Series 90-70/RX7i remote I/O and equipment-control networks.
- Process Automation — Distributed field I/O and PLC-to-PLC communications using Genius datagrams and Global Data.
The Genius bus can also support Series 90-70 remote drops, VersaMax Genius NIUs, and multiple PLC hosts.
Technical Pitfalls to Avoid
- Firmware matters on RX7i.
GE specifies firmware 5.9 or later for operation in PACSystems RX7i. The documented AB hardware revision is associated with firmware 6.0. Do not install an old firmware image into an RX7i system without checking the applicable firmware requirements. - Do not confuse with IC697BEM731.
Both are Genius Bus Controllers, but they belong to different physical module architectures. The is specifically a single-slot VME-style controller for RX7i/Series 90-70 configurations. - Check the Genius bus termination.
The electrical bus requires the appropriate termination resistance at both ends. GE documentation specifies 75, 100, 120, or 150 ohm termination depending on the applicable bus configuration. Incorrect termination can produce intermittent communication errors that resemble controller failure. - Do not exceed the practical bus-length limit for the selected baud rate.
The maximum distance changes with communication speed and cable type. A network that works at 38.4 kbaud may not remain reliable after being moved to 153.6 kbaud without checking the cable and topology. - Watch the single-channel limitation.
provides one Genius bus channel. If the application requires multiple independent Genius networks, additional Bus Controller modules or a different architecture may be required.
Related Products
- IC697BEM731 — Series 90-70 standard-width Genius Bus Controller. It performs a similar Genius communication role but uses the Series 90-70 standard-width module format. Do not assume physical interchangeability with the .
- IC687BEM734 — Genius Bus Controller variant used in RX7i/Series 90-70 architectures. It is relevant where the application requires the corresponding BEM734 configuration rather than the single-channel BEM731 arrangement.
- IC693BEM331 — Series 90-30 Genius Bus Controller. It belongs to the smaller Series 90-30 PLC family and is not a direct replacement for an RX7i .
- IC694BEM331 — PACSystems RX3i Genius Bus Controller. Useful for RX3i systems requiring Genius communications, but the rack and CPU architecture differ from RX7i.
- IC687BEM713 — RX7i/Series 90-70 Genius Bus Transmitter Module. This is a bus-expansion component rather than a replacement for the BEM731. GE documentation identifies it as a transmitter used for bus expansion.
- IC697BEM711 — Genius Bus Receiver Module for Series 90-70 expansion racks. It works with the bus-transmitter architecture rather than replacing the BEM731.
- IC697BEM733 — Series 90-70 Remote I/O Scanner. It provides a different role: interfacing a Series 90-70 remote drop with a host system rather than serving as the primary Genius Bus Controller.
- Genius I/O Blocks — Distributed Genius field I/O devices that can be connected to the . The controller supports individual Genius I/O blocks as well as other PLC and remote-I/O devices.
- PACSystems RX7i CPU Modules — The is installed in the RX7i rack alongside the CPU and other I/O/communication modules. GE identifies RX7i slots 2 through 17 as available installation positions for this Bus Controller.
