User`s guide

50 • Operation Theory
• Two programmable timer modes are provided:
Mode 0: Interrupt on Terminal Count
Mode 0 is typically used for event counting, as illustrated in fig 20. After the
initial count is written, OUT is initially low, and will remain low until the
Counter counts to zero. OUT then goes high and will remain high until a
new count is written into the Counter.
3 3 2 1 1 1 0 0 0
Gate
CLK
Count value
OUT
Mode 0, Initial count=3, Count down
Figure 20: Mode 0 Operation
Mode 1: Rate Generator
This mode operates like a divide-by-N counter, as illustrated in fig 21. After
the initial count is written, initially OUT is low. When the counter reaches 1,
OUT goes high for one clock pulse. OUT then goes low again. The counter
reloads the initial count and the process will be repeated.
3 3 2 2 1 3 2 1 3
Gate
CLK
Count value
OUT
mode 1, Initial count=3, Count down
Figure 21: Mode 1 Operation
Note: In Mode 1 the initial count value N must be larger than one.