HD6417641 RENESAS [Renesas Technology Corp], HD6417641 Datasheet - Page 209

• Manufacturer Part Number: HD6417641
• Manufacturer: RENESAS [Renesas Technology Corp]

5.2.3
The watchdog timer counter (WTCNT) and watchdog timer control/status register (WTCSR) are
more difficult to write to than other registers. The procedures for reading or writing to these
registers are given below.
Writing to WTCNT and WTCSR: These registers must be written by a word transfer
instruction. They cannot be written by a byte or longword transfer instruction. When writing to
WTCNT, set the upper byte to H'5A and transfer the lower byte as the write data, as shown in
figure 5.2. When writing to WTCSR, set the upper byte to H'A5 and transfer the lower byte as the
write data. This transfer procedure writes the lower byte data to WTCNT or WTCSR.
5.3
5.3.1
The WDT can be used to cancel standby mode with an interrupt such as an NMI interrupt. The
procedure is described below. (The WDT does not operate when resets are used for canceling, so
keep the RESETP or RESETM pin low until the clock stabilizes.)
1. Before transitioning to standby mode, always clear the TME bit in WTCSR to 0. When the
2. Set the type of count clock used in the CKS2 to CKS0 bits in WTCSR and the initial values for
3. The execution of a SLEEP instruction after the STBY bit of the standby control register
4. The WDT starts counting by detecting the edge change of the NMI signal.
TME bit is 1, an erroneous reset or interval timer interrupt may be generated when the count
overflows.
the counter in the WTCNT. These values should ensure that the time till count overflow is
longer than the clock oscillation settling time.
(STBCR: see section 6, Power-Down Modes) puts the system in standby mode and clock
operation then stops.
WTCNT write
WTCSR write
Address: H'A415FF84
Address: H'A415FF86
Notes on Register Access
Use of the WDT
Canceling Standbys
Figure 5.2 Writing to WTCNT and WTCSR
15
15
H'5A
H'A5
8
8
Rev. 4.00 Sep. 14, 2005 Page 159 of 982
7
7
Section 5 Watchdog Timer (WDT)
Write data
Write data
REJ09B0023-0400
0
0