Barnett Engineering B1474 Operation Manual page 12

– checks the chan nel, if this fea ture is en abled. If the chan nel is free, it as serts its PTT to
power up the ra dio's trans mit ter. If the chan nel is busy, it buff ers the re ceived data un til
the chan nel be comes free.
– pres ents MARK tone (car rier) onto the chan nel.
– sets its RTS/CTS de lay timer (from 20 to 300 msec). RTS/CTS de lay is a mis no mer in
this case as hand shak ing is not used. It is ac tu ally a buff er ing time be tween when the
mo dem starts re ceiv ing data from the com puter and when it starts trans mit ting.
RTS/CTS de lay must be greater than the car rier de tect de lay at the re ceiv ing end.
The mo dem at the re ceiv ing end senses car rier on the line and as serts its CD. The re ceived
data is muted for 5 or 50 msec to en sure that tran sients do not af fect the re ceived data.
At the send ing end, once the RTS/CTS de lay timer has ex pired, data is trans mit ted.
Re ceipt of any char ac ter from the send ing de vice, or trans mis sion of any buf fered char ac ter,
re starts the send ing mo dem's PTT drop de lay timer (from 0 to 250 msec).
Once the PTT drop de lay timer has ex pired, the mo dem re leases the ra dio trans mit ter and
re turns to re ceive 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 Hand shak ing, Non-Buffered
Basic operation and timing with no handshaking, no data buffering are as follows:
RTS is al ways as serted. Do not con nect the hard ware RTS.
PTT is al ways as serted, i.e. the ra dio's car rier is al ways on. There is no RTS/CTS de lay or
PTT drop de lay.
Data gen er ated by the send ing de vice is passed di rectly through the mo dem with out hand -
shak ing, buff er ing or time de lays. Data may be any for mat.
For no handshaking, non-buffered operation, set XON/XOFF signaling off, assert RTS
(continuous) on, and buffering off. Do not connect the hardware RTS and CTS, and do not set
RTS/CTS or PTT drop delays.
B1474 BARNETT EN GI NEERING LTD. PAGE 11