Microcomputer Circuits and Processes

It does this by outputting a signal from the SAR to the CPU's
interrupt pin, here labelled 'INT 1'.As mentioned earlier, this causes the
CPU to jump to a subroutine to input the result of the conversion. The
'interrupt' will interrupt any other task the CPU may be busy with, like
scanning the keyboard, or writing a number into the display. Finally,
when the conversion is complete, the binary number must be enabled
on to the bus, and read, by the CPU. So an INput signal must be
generated, which is a read; this is done by ANDing decoder output
number 7 with RD, and this signal is used to enable the buffer.
You can now think out the remaining chunks of the circuit for
yourself, guided by the idea that to switch on, or enable, any chunk of
the circuit, you must AND a decoder output with an RD if the chunk is
an INput, or AND a decoder output with a WR if the chunk is an
OUTput.
Here are a couple of applications of CONDAC in the laboratory.
The first, shown in figure 4.39, is a study of animal behaviour. Variables
to be measured are temperature, level of food in the trough, and level of
water in the bottle. The computer has to control the heating of the cage
and the level of light in the cage. The last two are easily arranged: a
D-to-A port is used to drive a heater and a second D-to-A to drive a
lamp. Power amplifiers will be needed to drive lamp and heater, since
both will need more current than a pure D-to-A converter can provide.
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