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5. COUNTER/TIMERS
The ZT
8904 includes one Intel-compatible 8254 device with a total of three
programmable counter/timers. The counter/timers are useful for software timing loops,
timed interrupts, and periodic interrupts. The major features of the counter/timers are
listed below.
•
Three 16-bit counter/timers
•
Six programmable operating modes
•
Binary and BCD counting
•
Interrupt and polled operation
The counter/timer architecture is illustrated in the "Counter/Timer Architecture" figure
below. In some cases, not all counter/timers are available for application development.
In an MS DOS system, for example, counter/timer 0 generates a periodic system
interrupt and should not be programmed by the application. Please refer to the selected
operating system manual for more information.
TIMER 0
GATE0
CLK0
OUT0
INTERRUPT IR0
1.19318 MHz
LOGICAL ONE
TIMER 1
GATE1
CLK1
OUT1
INTERRUPT IR10 OR
1.19318 MHz
LOGICAL ONE
TIMER 2
GATE2
CLK2
OUT2
INTERRUPT IR11 OR
1.19318 MHz
LOGICAL ONE
DMA CHANNEL 0
DMA CHANNEL 1
Counter/Timer Architecture