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HARDWARE
FUNCTIONAL DESCRIPTION
3874 Group User’s Manual
Fig. 25 Structure of timer X mode register
Timer X
Timer X is a 16-bit timer that can be selected in one of four modes
and can be controlled the timer X write and the real time port by
setting the timer X mode register.
(1) Timer Mode
The timer counts f(XIN)/16 (or f(XCIN)/16 in system clock
φ = XCIN/
2).
(2) Pulse Output Mode
Each time the timer underflows, a signal output from the CNTR0
pin is inverted. Except for this, the operation in pulse output mode
is the same as in timer mode. When using a timer in this mode, set
the direction register of corresponding port to output mode.
(3) Event Counter Mode
The timer counts signals input through the CNTR0 pin.
Except for this, the operation in event counter mode is the same
as in timer mode.
(4) Pulse Width Measurement Mode
The count source is f(XIN)/16 (or f(XCIN)/16 in system clock
φ =
XCIN/2. If CNTR0 active edge switch bit is “0”, the timer counts
while the input signal of CNTR0 pin is at “H”. If it is “1”, the timer
counts while the input signal of CNTR0 pin is at “L”.
s Notes
q Timer X write control
If the timer X write control bit is “1”, when the value is written in the
address of timer X, the value is loaded only in the latch. The value
in the latch is loaded in timer X after timer X underflows.
If the timer X write control bit is “0”, when the value is written in the
address of timer X, the value is loaded in the timer X and the latch
at the same time.
When the value is to be written in latch only, if the value is written
to the latch at timer X underflows, the value is consequently
loaded in the timer X and the latch at the same time. Unexpected
value may be set in the high-order counter when the writing in
high-order latch and the underflow of timer X are performed at the
same timing.
q CNTR0 interrupt active edge selection
CNTR0 interrupt active edge depends on the CNTR0 active edge
switch bit.
q Real time port control
Data for the real time port are output from ports P56 and P57 each
time the timer X underflows. (However, if the real time port control
bit is changed from “0” to “1”, data are output independent of the
timer X operation.) When the data for the real time port is changed
while the real time port function is valid, the changed data are out-
put at the next underflow of timer X.
Before using this function, set the corresponding port direction
registers to output mode.
Timer X mode register
(TXM : address 002716)
Timer X write control bit
0 : Write value in latch and counter
1 : Write value in latch only
Real time port control bit
0 : Real time port function invalid
1 : Real time port function valid
P56 data for real time port
P57 data for real time port
Timer X operating mode bits
b5 b4
0
0 : Timer mode
0
1 : Pulse output mode
1
0 : Event counter mode
1
1 : Pulse width measurement mode
CNTR0 active edge switch bit
0 : Count at rising edge in event counter mode
Start from “H” output in pulse output mode
Measure “H” pulse width in pulse width
measurement mode
Falling edge active for CNTR0 interrupt
1 : Count at falling edge in event counter mode
Start from “L” output in pulse output mode
Measure “L” pulse width in pulse width
measurement mode
Rising edge active for CNTR0 interrupt
Timer X stop control bit
0 : Count start
1 : Count stop
b7
b0