NEC PD754144 - Manual (Page 175)

CHAPTER 6 PERIPHERAL HARDWARE FUNCTION
175 User’s Manual U10676EJ3V0UM
(3) Notes on changing count pulse
When it is specified to change the count pulse (CP) by rewriting the contents of the timer counter mode register
(TMn), the specification becomes valid immediately after execution of the instruction that commands the
specification.
Clock A specification Clock B specification
Rewrite instruction Rewrite instruction
Clock A specification
Clock A
Clock B
Count pulse (CP)
A whisker-like CP (<1> or <2 > in the figure below) may be generated depending on the combination of the
clocks for changing CP. In this case, a miscount may occur or the contents of the count register (Tn) may
be destroyed. To change CP, be sure to set the bit 3 of TMn bit to “1” and restart the timer at the same time.
Clock A specification Clock B specification
Rewrite instruction Rewrite instruction
Clock A specification
Clock A
Clock B
Count pulse (CP)
<1> <2>
Remark n = 0 to 2