BASIC PROORAHHING SECTION 4. 11
protocols, etc, have been finalised. Such sequences can present
inputs
to the mainframe and inspect the reply for keywords like
'READY' or simple cursor prompts.
NOTE: Many mainframes are unpredictable in the response they
provide to login sequences, with variable 'welcome' or 'news'
messages. Make sure your automatic sequence is robust enough to
handle these eventualities!
Some general points about database communications should be
noted:
4.11.4.1
Rate
Communication occurs generally at 300 baud, although other
configurations are possible, Remember that the screen
character generator will display all ASCII characters, even if
they are not shown on the keyboard,
Other rates encountered on dial-up systems are 110 (very rare)
and 1200, but only with sophisticated modems.
4.11.4.2 Parity
Dial-up systems can expect any of even, odd or no parity
selections. Transmit and receive parities are generally the
same. Always use receive parity if it is available - the
occasional appearance of the parity error symbol is a useful
indication of bad lines, Remember that telephone lines can be
bad in one direction only.
4,11.4,3 Full/Half Duplex
VER.V09F
Database systems vary widely in the use of full or half duplex
operation.
Full duplex occurs when the host system 'echoes' every received
character back to HUNI'ER. In this mode, HUNTER's transmission
echo should be selected 'off' so that characters typed on the.
keyboard only appear on the screen if they have completed the
whole circuit of HUNTER - Mainframe - HUNTER,
Basic routines can check full duplex replies as an absolutely
secure communication protocol, provided the mainframes' own
messages don't confuse the issue,
PAGE 4 - 39
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