Computer Interfacing

Conversion between digital and analogue

output would also provide the status level output to the

computer. The binary value held by the counter/regis-

ter is the equivalent of the analogue input. The process

would repeat on receipt of a new start convert pulse.

This is one of the slower types of converter. The length

of the conversion process depends upon the size of the

analogue input. For an analogue input voltage equal to

the full scale input, the counter has to count up to its

limit. An N-bit counter needs (2

N

- 1) clock cycles to com-

plete the conversion. An

8-bit

counter using a 1 MHz

clock would take (2

8

- 1) microseconds, = 255 μ8 t