Black Box Short-Haul Modem B, ME810, ME800A-R2, ME805-C-R2 manual Flow Control

SHM-B ASYNC

3.4 Flow Control

The SHM-B uses a clever, yet simple way to allow this unit to work with a broad line of equipment.

STANDARD EIA-232C HANDSHAKING (RTS/DTR CONTROL

JUMPER IN EN POSITION)

The individual SHM-B modems force their own DTR, RTS, CTS, and DSR control lines HIGH (>+3V) when:

•The twisted-pair wires are installed correctly.

•Power is applied to both modems.

•No computer devices are attached to the modems.

This forces DCD HIGH on the remote modem; thus, the remote modem knows to expect data. In this state, “all systems are go.” The only way this state changes is if your equipment overrides this condition. For example, if your equipment drops DTR to a NEGATIVE signal, your equipment’s DTR being low will override the SHM-B’s DTR, and DCD on the remote modem will go LOW.

14