All INMC correspondence should be addressed to:
c/o Nascom Microcomputors Ltd
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Herts ___ ___
NASCOM I – Various Technical Notes
Floating Inputs to PORT 0. Keyboard user in puts.
Although the software ignores spurious characters which
may appear on PORT 0, the keyboard routine still carries
out a search to determine whether the input was valid. If,
as is likely, the two user inputs on SKT 1 are left unconnected,
this could have a detrimental effect on the
running of any program with interactive keyboard routines.
For example, as B-BASIC V1.1 scans the keyboard for change
at the end of each statement, any spurious input to PORT 0,
will cause the keyboard routine to ‘waste time’ searching
for a character which does not appear in the keyboard lookup
table. This has the undesirable effect of making a
‘FOR – NEXT’ timing loop vary with each spurious character
detected, causing imprecise timings.
This flaw may be easily rectified by connecting the two
user inputs to +5 volts, forcing them permanently ‘high’.
Under these circumstances, no spurious inputs occur.
The effective speed of Load and Dump (and Read and Write}
may be doubled by connecting the UART clock link to pin 12
of IC2 (it is normally connected to pin 11 of IC2, via the
UART clock link). This modification has been found to
work on the majority of Nascoms; further, on some Nascoms
it has been found that the speed may be doubled yet again
by connecting the link to pin 13 of IC2. It should be noted
that these modifications are not ‘guaranteed’ to work.
Adjustment of the 1760Hz (10 chars./sec.) UART clock, without
test equipment. Firstly, it should be noted that this clock
need not be adjusted until such time as a printer or other
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