2-24
Functional Description
●
Hardware-triggered strobe (Mode 5) - The output is initially high.
A rising edge of the gate input acts as a trigger. The counter is loaded
with the initial count value on the next clock pulse after the trigger,
but the counter does not start counting. At the next clock pulse, the
counter starts counting down. When the counter reaches zero, the
output goes low for one clock pulse and then goes high again. Note
that the output does not go low until n + 1 clock pulses after the
trigger event occurs, where n indicates the loaded count.
After the trigger event occurs, the gate input has no effect on the
output. Writing a new value during counting does not affect the
counting sequence.
Figure 2-11 illustrates hardware-triggered strobe mode.
Figure 2-11. Hardware-Triggered Strobe Mode
Refer to 8254 documentation for information on programming the 8254
counter/timer circuitry for general-purpose tasks. Table 2-2 lists several
companies that provide documentation for the 8254.
Clock pulse
Output
Counter is loaded with
initial count value of 3
Rising edge of gate
input acts as trigger
3
2
1
