Specifications

24 •• Operation Theorem

The digital OUT operation is:

outport (BASE+14, 0xAAAAAAAA ) // (A : 0 ~ F)

The digital IN operation is:

value = inport (BASE+10) // The input status is save in the

// value variable

4.2 Timer Pacer Mode

The digital I/O access control is clocked by timer pacer, which is

generated by a interval programming timer/counter chip 8254.

There are three timers on the 8254. The timer 0 is used to

generate timer pacer for digital input, and timer 1 is used for digital

output. The configuration is illustrated as below.

Timer 0

Timer 1

Timer 2

CLK0

GATE0

OUT0

CLK1

GATE1

CLK2

GATE2

OUT1

OUT2

8254 Timer/Counter

Digital Input Timer Pacer

Digital Output Timer Pacer

4MHz Clock

“H”