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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
The General Purpose Timer Units
User’s Manual
14-9
V2.2, 2004-01
GPT_X1, V2.0
Gated Timer Mode
Gated timer mode for the core timer T3 is selected by setting bitfield T3M in register
T3CON to 010
B
or 011
B
. Bit T3M.0 (T3CON.3) selects the active level of the gate input.
The same options for the input frequency are available in gated timer mode as in timer
mode (see
). However, the input clock to the timer in this mode is gated
by the external input pin T3IN (Timer T3 External Input).
To enable this operation, the associated pin T3IN must be configured as input, that is,
the corresponding direction control bit must contain 0.
Figure 14-5
Block Diagram of Core Timer T3 in Gated Timer Mode
If T3M = 010
B
, the timer is enabled when T3IN shows a low level. A high level at this line
stops the timer. If T3M = 011
B
, line T3IN must have a high level in order to enable the
timer. Additionally, the timer can be turned on or off by software using bit T3R. The timer
will only run if T3R is 1 and the gate is active. It will stop if either T3R is 0 or the gate is
inactive.
Note: A transition of the gate signal at pin T3IN does not cause an interrupt request.
Prescaler
Gate
Ctrl.
Core Timer T3
Toggle Latch
MCB05392
BPS1
T3I
MUX
Up/Down
0
1
T3EUD
f
GPT
=1
T3UD
f
T3
T3R
Count
T3OUT
T3IRQ
to
T2/T4
T3UDE
T3IN