Barnett Engineering B1474 operation manual No Handshaking

No Handshaking

Basic operation and timing with data buffering (no handshaking) in a trunking system is as follows:

∙The sending computer begins sending data. Data format must be 8 bits, no parity, 1 stop bit.

∙Upon receiving data, the modem performs the following:

–checks the channel for RFCTS - if the channel has been assigned already, it asserts

its PTT to power up the radio’s transmitter. If the channel is busy, it asserts PTT to ob- tain the channel and buffers the received data until the channel becomes assigned.

–presents tones onto the channel.

–sets its RTS/CTS delay timer.

∙The receiving modem senses carrier on the line and asserts its CD. The received data is muted for 5 or 50 msec to ensure that transients do not affect the received data.

∙After the RTS/CTS delay timer has expired, data is transmitted.

∙Receipt of any character or transmission of any buffered character restarts the modem’s PTT drop delay timer.

∙Once the modem stops receiving characters and the PTT drop delay timer expires, the mo- dem releases the radio transmitter and returns to receive mode.

This configuration can buffer 500 msec worth of characters. To prevent internal data buffer overflow, it is important that the radio system will be available within 500 msec (RTS/CTS delay plus maximum channel busy time) or the maximum amount of buffered data is less than 50 characters.

B1474 BARNETT ENGINEERING LTD. PAGE 25