Barnett Engineering B1474 operation manual LED Control, XON / Xoff Controls, Squelch Polarity

GND (Chassis)	Pin 1
TXD	Pin 2
RXD	Pin 3	(connect only if using hardware handshaking)
RTS	Pin 4
CTS	Pin 5	(connect only if using hardware handshaking)
GND (Signal)	Pin 7
CD	Pin 8

The cable and housing on the DB-25S socket must be shielded to conform to FCC, part 15-J/A standards for emissions. Using a non-shielded cable may result in undesirable radio interference.

(3) DIP SWITCH SETTINGS

The following section describes the function of each DIP switch on the modem. The settings are summarized in a table in Section 7 - Configuration.

LED Control

The LED indicators may be disabled to conserve power. Set SW1.1 OFF to disable the LEDs.

RTS/CTS Delay

When the sending device requests transmission, a preset delay is inserted before the modem transmits. This delay allows the two-way radio to warm up, or, on a cable system, allows the tones to settle on the channel before data transmission begins. When hardware handshaking is used, the modem pauses the sending device by delaying return of the CTS signal. When XON/OFF or no handshaking are used, the RTS/CTS delay specifies the amount of data which will be buffered. Set DIP switches SW1.2, SW1.3, and SW1.4 for the desired delay, from 20 to 1000 msec, as specified in Section 7 - Configuration.

PTT Drop Delay

When transmission is no longer requested by the sending computer, a selectable delay is inserted before the PTT on the radio is released. This delay prevents the squelch tail at the receiving radio from interfering with the data. Set DIP switches SW1.5, SW1.6, and SW1.7 for the desired drop delay, between 0 and 500 msec, as specified in Section 7 - Configuration.

XON / XOFF Controls

SW1.8 controls whether the modem will send XON and XOFF to the sending computer when the radio channel is busy (software handshaking). If the sending computer does not understand these characters, the switch must be OFF.

Squelch Polarity

If the modem is connected to a radio, the channel can be monitored for RF carrier. SW1.9 is changed depending upon the polarity of the carrier operated switch (COS) signal. If the COS goes high when carrier is present, and low when the channel is free, set SW1.9 OFF. If the opposite occurs, set SW1.9 ON. While the channel is busy, the modem will wait, sending only when the channel is clear.

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