UPD780957 Datasheet, PDF (173/326 Pages) NEC – 8-Bit Single-Chip Microcontrollers

CHAPTER 9 8-BIT TIMERS 80 TO 83
9.6 Operating Cautions for 8-Bit Timers 80 to 83
(1) Timer start errors
An error of up to one clock may occur in the time required for a match signal to be generated after timer start.
This is because 8-bit timer counter 8n (TM8n: n = 0 to 3) starts operation asynchronously to the count pulse.
Figure 9-7. Start Timing of 8-Bit Timer Counter 8n (TM8n)
Count clock
TM8n count value
00H
01H
02H
03H
04H
Count start
n = 0 to 3
(2) Cautions during timer count operation
(a) 8-bit compare register 8n (CR8n)
Do not rewrite CR8n during a timer count operation. Rewriting is possible, however, if the value to be
written is the same as the one before rewrite.
Timer count operation must be stopped (by setting TCE8n to 0) before rewriting a CR8n value.
(b) Bits 0 and 1 (TCL8n0 and TCL8n1) of 8-bit timer control register 8n (TMC8n)
Do not write a value to bits 0 and 1 (TCL8n0 and TCL8n1) of 8-bit timer control register 8n (TMC8n)
during a timer count operation.
Timer count operation must be stopped (by setting TCE8n to 0) before setting TCL8n0 and TCL8n1.
Remark n = 0 to 3
User’s Manual U13655EJ2V1UD
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