8253 Programmable Interval Timer Register usage 19880619/WJ van Ganswijk 0 rw counter 0 1 rw counter 1 2 rw counter 2 3 w write mode word 00...... select counter 0 01...... select counter 1 10...... select counter 2 11...... illegal ..00.... counter latching operation ..01.... read/load least significant byte only ..10.... read/load most significant byte only ..11.... read/load least significant byte first, than most ... ....000. mode0: interrupt on terminal count ....001. mode1: programmable one-shot ....x10. mode2: rate generator ....x11. mode3: square wave rate generator ....100. mode4: software triggered strobe ....101. mode5: hardware triggered strobe .......1 binary coded decimal (bcd) counter (4 decades) *end