Section 13 Timer Z
1. Free-running count operation and periodic count operation
Immediately after a reset, the TCNT counters for channels 0 and 1 are all designated as free-
running counters. When the relevant bit in TSTR is set to 1, the corresponding TCNT counter
starts an increment operation as a free-running counter. When TCNT overflows, the OVF flag
in TSR is set to 1. If the value of the OVIE bit in the corresponding TIER is 1 at this point,
timer Z requests an interrupt. After overflow, TCNT starts an increment operation again from
H'0000.
Figure 13.8 illustrates free-running counter operation.
TCNT value
H'FFFF
H'0000
Time
STR0,
STR1
OVF
Figure 13.8 Free-Running Counter Operation
When compare match is selected as the TCNT clearing source, the TCNT counter for the relevant
channel performs periodic count operation. The GR registers for setting the period are designated
as output compare registers, and counter clearing by compare match is selected by means of bits
CCLR1 and CCLR0 in TCR. After the settings have been made, TCNT starts an increment
operation as a periodic counter when the corresponding bit in TSTR is set to 1. When the count
value matches the value in GR, the IMFA, IMFB, IMFC, or IMFD flag in TSR is set to 1 and
TCNT is cleared to H'0000.
If the value of the corresponding IMIEA, IMIEB, IMIEC, or IMIED bit in TIER is 1 at this point,
the timer Z requests an interrupt. After a compare match, TCNT starts an increment operation
again from H'0000.
Figure 13.9 illustrates periodic counter operation.
Rev. 3.00 Sep. 10, 2007 Page 224 of 528
REJ09B0216-0300
RENESAS [ RENESAS TECHNOLOGY CORP ]
