There are three countdown timers in the 83+ SE. Each one consists of three ports. Refer to the following table:

		On/off port	Loop control	Counter

Timer1		30		31		32
Timer2		33		34		35
Timer3		36		37		38


Each timer is independent of the others. You can either activate the timer in an endless counting, or set it a number to countdown and stop.

Speed values:

42h - 100 Hz
43h - 10 Hz
47h - 8 Hz

To start the timer:

To the on/off port, output a speed value above, to the loop control port output 00h, to the counter port output 0FFh. 42h is for a faster speed than 43h.

To start the timer with a countdown:

To the on/off port, output a speed value above, to the loop control port output 00h, to the counter port output the number to countdown from. Timer will countdown and then stop.