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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
The General Purpose Timer Units
User’s Manual
14-10
V2.2, 2004-01
GPT_X1, V2.0
Counter Mode
Counter Mode for the core timer T3 is selected by setting bitfield T3M in register T3CON
to 001
B
. In counter mode, timer T3 is clocked by a transition at the external input pin
T3IN. The event causing an increment or decrement of the timer can be a positive, a
negative, or both a positive and a negative transition at this line. Bitfield T3I in control
register T3CON selects the triggering transition (see
Figure 14-6
Block Diagram of Core Timer T3 in Counter Mode
For counter mode operation, pin T3IN must be configured as input (the respective
direction control bit DPx.y must be 0). The maximum input frequency allowed in counter
mode depends on the selected prescaler value. To ensure that a transition of the count
input signal applied to T3IN is recognized correctly, its level must be held high or low for
a minimum number of module clock cycles before it changes. This information can be
found in
Table 14-2
GPT1 Core Timer T3 (Counter Mode) Input Edge Selection
T3I
Triggering Edge for Counter Increment/Decrement
0 0 0
None. Counter T3 is disabled
0 0 1
Positive transition (rising edge) on T3IN
0 1 0
Negative transition (falling edge) on T3IN
0 1 1
Any transition (rising or falling edge) on T3IN
1 X X
Reserved. Do not use this combination
MCB05393
Core Timer T3
Toggle Latch
MUX
Up/Down
0
1
T3EUD
T3IN
=1
T3UD
T3R
Count
T3OUT
T3IRQ
to
T2/T4
T3UDE
T3I
Edge
Select