UPD784938 Datasheet, PDF (378/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 12 TIMER 3
12.4 Timer Counter 3 (TM3) Operation
12.4.1 Basic operation
Timer 3 can operate in an 8-bit or 16-bit mode. These operation modes are selected by bit 4 (BW3) of timer control
register 0 (TMC0)^Note.
In the timer 3 count operation, the count-up is performed using the count clock specified by the high-order 4 bits of
prescaler mode register 0 (PRM0).
When RESET is input, timer counter 3 (TM3) is cleared to 0000H, and the count operation is stopped.
Count operation enabling/disabling is controlled by bit 7 (CE3) of timer control register 0 (TMC0) (the high-order 4 bits
of TMC0 control timer 3 operation). When the CE3 bit is set (to 1) by software, the contents of TM3 are immediately cleared
on the first count clock, and then the count-up operation is performed. When the CE3 bit is cleared (to 0), TM3 becomes
0H immediately, and match signal generation is stopped. If the CE3 bit is set (to 1) again when it is already set (to 1), TM3
continues the count operation without being cleared.
Note Unless there functional differences are found, the register names in the 8-bit mode are used. In the 16-bit mode,
the register names TM3 and CR30 are TM3W and CR30W, respectively.
Figure 12-4. Basic Operation in 8-Bit Operation Mode (BW3 = 0)
(a) Count started → count stopped → count started
Count clock
TM3 0H 0H 1H 2H
0FH 10H 11H
0H
0H 1H
CE3
Count started
CE3 ← 1
Count stopped
CE3 ← 0
(b) When “1” is written to the CE3 bit again after the count starts
Count clock
Count started
CE3 ← 1
TM3 0H 0H 1H 2H 3H 4H 5H 6H
CE3
Count started
CE3 ← 1
Rewrite
CE3 ← 1
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Preliminary User’s Manual U13987EJ1V0UM00