Center-Aligned Modes - Intel 8XC196MC User Manual

9.3.5.1

Center-aligned Modes

In the center-aligned modes, the counter counts down from the WG_RELOAD value to 1, then
counts back up from 1 to WG_RELOAD. When you write to the WG_RELOAD register,
WG_COUNTER is loaded with the reload value. When you set the enable bit in the control reg-
ister, the counter begins counting down and continues counting until it reaches 1, waits one state
time, and starts counting up until it reaches WG_RELOAD. At this point, WG_RELOAD is up-
dated and WG_COUNTER is reloaded with the updated value, so a new reload value takes effect
for the next cycle. The counter resumes counting down from WG_RELOAD to 1. This produces
a symmetrical ascending and descending count, illustrated by the triangular wave in Figure 9-4,
with a period that is twice the WG_RELOAD value. Figure 9-5 shows the operation of outputs
and interrupts in center-aligned modes.
Counter
Enabled
WG_COUNTER
Value
1
0
Reset
Figure 9-4. Center-aligned Modes — Counter Operation
In mode 0, the WG_COMPx and WG_OUTPUT registers are updated only once during the car-
rier period, when the counter reaches the reload value. In mode 1, these registers are updated
twice during the carrier period: first when the counter is set to 1, then again when it reaches the
reload value.
WG_COUNTER =
WG_RELOAD
Write to WG_RELOAD
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WAVEFORM GENERATOR
WG_RELOAD
Changed
Carrier Period
A2636-01
9-9