GE IS200ISBBG1A ISBus Bypass Board
Description:
The IS200ISBB—GE’s ISBus Bypass Board, commonly shortened to ISBB—installs between an ISBus full-duplex source (either a BAlA or ACL module) and the ISBus itself. Its key function is to bypass an ISBus node in two specific scenarios: when the node loses power, or when the interlock within the full-duplex interface is opened.

A bypass relay is integrated into the ISBB. When 24V DC power is available (supplied through either P1 or P4) and the interlock on P1 is closed, this relay routes transmit signals from the full-duplex input (P1) to both the transmit output (P2) and the receive data input (P3) of the ISBus.

If the ISBB is not supplied with 24V DC power, three critical connection changes take place:
- The transmit connection between P1 and P2 is cut off.
- The receive connection between P3 and P1 is disconnected.
- A new connection is established between the receive input (P3) and transmit output (P2): specifically, RECV DATA IN+ links to XMIT DATA OUT+, and RECV DATA IN- links to XMIT DATA OUT-.

Two LED indicators are included on the ISBB. One shows the status of the transmit data input, while the other indicates whether the bypass relay has power.

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