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V. PROGRAMMING CONSIDERATIONS
PROGRAMMING THE BUFFERS
Service Rate
When servicing transmission lines on a bit basis there are certain timing factors which must
be taken into account.
The following table shows the service rate for six standard teletype
transmission speeds:
Bits per Second
45
50
56.25
75
110
150
Service Rate (milliseconds)
22.2
20.0
17. 7
13.3
9.09
6.67
In
each case, the service rate can be defined as the operation of the receive or transmit flag
of the bit buffer.
When scanning the bit buffers, the service rate is taken into account and the Program Interrupt
Executive initiates scanning at a rate slightly faster than the service rate. For a 45-bit/ second
transmission line having a service time of 22.2 milliseconds, the line would be scanned approxi-
mately every 21.0 milliseconds to ensure that any speed variations in the remote terminal
would not result in
data
lost at the DATANET-30.
Basic Program Cycle
A real time program response time to certain events must be very small. The communications
programs must be divided into the following events:
1.
Receive bits
2.
Assemble bits into characters
@&IT&~~lrc:J ~@------------
V-1
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