Software Handshaking Using XON/XOFF
Basic operation and timing using XON/XOFF software handshaking in a trunking system is as follows:
∙The sending computer begins sending data. The format must be 8 data bits, no parity, 1 stop bit.
∙Upon detecting data, the sending modem performs the following:
– checks the channel. If RFCTS has already been assigned (the channel is available), it as- serts its PTT to power up the radio’s transmitter. If the channel has not been assigned yet, it sends XOFF to the sending computer and asserts PTT to obtain the channel. When the channel gets assigned, it sends XON to the computer and continues.
– 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.
∙Whenever the modem receives a character from the sending device or transmits any buf- fered character, it restarts the PTT drop delay timer.
∙Once the modem stops receiving characters and the PTT drop delay timer has expired, the modem 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 RTS/CTS delay timer be set to a value less than 500 msec and that the computer respond immediately to an XOFF command.
B1474 | BARNETT ENGINEERING LTD. | PAGE 24 |
