Hardware Reference
In-Depth Information
The circuit connection for the period measurement is shown in Figure 8.15, and the logic flow
for the period measurement is shown in Figure 8.16.
68HC12
PT0
1 period
Figure 8.15
■
Period measurement signal connection
Start
Choose to capture the rising edge
Set the timer counter prescale factor to 64
Enable the timer counter
Clear the C0F flag
No
C0F = 1?
Ye s
Save the captured first edge
Clear the C0F flag
No
C0F = 1?
Ye s
Take the difference of the second and
the first captured edges
Stop
Figure 8.16
■
Logic flow of period measurement
The assembly program that measures the period using this method is as follows:
#include
“c:\miniide\hcs12.inc”
org
$1000
edge_1st
rmb
2
; memory to hold the first edge
period
rmb
2
; memory to store the period
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