Spring 1979, Issue 2

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All INMC correspondence should be addressed to:

The Editor
INMC Newsletter
c/o Nascom Microcomputors Ltd
___ ____ ______
Herts ___ ___

Yours sincerely

Dave Hunt

NAS­COM IVarious Technical Notes

  1. 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.

  2. UART clocks.

    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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