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No Hand shak ing
Basic operation and timing with data buffering (no handshaking) in a trunking system is as
follows:
The send ing com puter be gins send ing data. Data for mat must be 8 bits, no par ity, 1 stop bit.
Upon re ceiv ing data, the mo dem per forms the fol low ing:
–
checks the chan nel for RFCTS - if the chan nel has been as signed al ready, it as serts
its PTT to power up the ra dio's trans mit ter. If the chan nel is busy, it as serts PTT to ob -
tain the chan nel and buff ers the re ceived data un til the chan nel be comes as signed.
–
pres ents tones onto the chan nel.
–
sets its RTS/CTS de lay timer.
The re ceiv ing mo dem 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.
Af ter the RTS/CTS de lay timer has ex pired, data is trans mit ted.
Re ceipt of any char ac ter or trans mis sion of any buf fered char ac ter re starts the mo dem's PTT
drop de lay timer.
Once the mo dem stops re ceiv ing char ac ters and the PTT drop de lay timer ex pires, 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 is less than
50 characters.
B1474
BARNETT EN GI NEERING LTD.
PAGE 25
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