HD64F3670 Datasheet, PDF (158/305 Pages) Renesas Technology Corp – Hitachi Single-Chip Microcomputer

11.4 Operation
• Normal Operation
• PWM Operation
11.4.1 Normal Operation
TCNT performs free-running or periodic counting operations. After a reset, TCNT is set as a free-
running counter. When the CST bit in TMRW is set to 1, TCNT starts incrementing the count.
When the count overflows from H'FFFF to H'0000, the OVF flag in TSRW is set to 1. If the OVIE
in TIERW is set to 1, an interrupt request is generated. Figure 11-2 shows free-running counting.
TCNT value
H'FFFF
H'0000
Time
CST bit
OVF
Flag cleared
by software
Figure 11-2 Free-Running Counter Operation
Periodic counting operation can be performed when GRA is set as an output compare register and
bit CCLR in TCRW is set to 1.
When the count matches GRA, TCNT is cleared to H'0000, the IMFA flag in TSRW is set to 1. If
the corresponding IMIEA bit in TIERW is set to 1, an interrupt request is generated. TCNT
continues counting from H'0000. Figure 11-3 shows periodic counting.
Rev. 1.0, 03/01, page 134 of 280