Acorn BBC Master 128, Руководство по обслуживанию

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Master Series Service Manual
nKBEN:- Generated by the system VIA, this line is taken active low to
enable the row and column addresses to be determined by the Operating
System.
MHz1:- This is the timing reference.
SWT1, RST0:- These connections are not
used. The Keyboard Matrix
The keys are physically arranged as a QERTY type keyboard with 10
function keys, 4 cursor control keys and a 19 key numeric keypad.
The matrix is as follows:-
Figure 5
Sound Generator
The sound generator is an SN7694A device. Three sound channels plus
one pseudo random noise channel are provided. The full description of
it is found in the manufacturers data sheet. It is provided with a
reference clock of 4MHz from central timing. The output is filtered as
described in the section 'Audio Circuitry'.
The output can also be connected by screened cable to the optional
modem. This output is mixed on the modem board to generate dialling
tones for DTMF exchanges where the modem hardware does not provide
such tones itself.
20 Issue 1