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SHM-B PLUS ASYNC
2. Introduction
The Short-Haul Modem Model B Async Plus (SHM-B
Async) is an asynchronous full-duplex 4-wire line
driver/receiver which allows two EIA-232 devices to
communicate at distances of up to 4 miles and at data
speeds of up to 115.2 kbps. In addition to the
transmitter and receiver circuits, the SHM-B Async Plus
includes EIA-232 control line interfaces, status monitor
LEDs, and a loopback switch. The SHM-B is available as
a standalone version (ME800A-Plus).
The SHM-B is designed to operate over a 4-wire metallic
circuit. Optimum performance is obtained with twisted-
pair cable (see specifications). Most types of twisted-pair
cable may be used, often with little or no performance
degradation.
The SHM-B Async is designed for maximum operator
safety. There are no voltages greater than 12 VDC or 16
VAC present on the circuit board of the unit. The
Receive lines are protected from potential ground
differences through optical isolators rated at 1500 volts.
