–checks the channel, if this feature is enabled. If the channel is free, it asserts its PTT to power up the radio’s transmitter. If the channel is busy, it buffers the received data until the channel becomes free.
–presents MARK tone (carrier) onto the channel.
–sets its RTS/CTS delay timer (from 20 to 300 msec). RTS/CTS delay is a misnomer in this case as handshaking is not used. It is actually a buffering time between when the modem starts receiving data from the computer and when it starts transmitting.
RTS/CTS delay must be greater than the carrier detect delay at the receiving end.
∙The modem at the receiving end 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.
∙At the sending end, once the RTS/CTS delay timer has expired, data is transmitted.
∙Receipt of any character from the sending device, or transmission of any buffered character, restarts the sending modem’s PTT drop delay timer (from 0 to 250 msec).
∙Once 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 radio system will be available within 500 msec (RTS/CTS delay plus maximum channel busy time) or the maximum amount of buffered data be less than 50 characters.
For no handshaking, buffered operation, set XON/XOFF signaling off, assert RTS (continuous) off, and buffering on. Do not connect the hardware RTS and CTS. Set RTS/CTS delay and PTT drop delay as required.
No Handshaking, Non-Buffered
Basic operation and timing with no handshaking, no data buffering are as follows:
∙RTS is always asserted. Do not connect the hardware RTS.
∙PTT is always asserted, i.e. the radio’s carrier is always on. There is no RTS/CTS delay or PTT drop delay.
∙Data generated by the sending device is passed directly through the modem without hand- shaking, buffering or time delays. Data may be any format.
For no handshaking,
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