17 WATCHDOG TIMER (WDT)
17-4
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
External NMI Output
17.4.6
The watchdog timer can output the NMI signal generated to external devices. The watchdog timer uses the #WDT_
NMI pin for this output. Setting NMIEN/WD_EN register to 1 enables the external NMI signal output as well as the
internal NMI signal output. When the watchdog timer counter reaches the comparison data, the #WDT_NMI pin
outputs a low pulse with 32 input clock cycles.
Input clock
Counter data
Comparison data
#WDT_NMI output
FFFF1D FFFF1E FFFF1F FFFF20
FFFF20
32 input clock cycles
0
1
2
1E
1F
20
21
22
4.6.1 External NMI Output
Figure 17.
Control Register Details
17.5
5.1 List of WDT Registers
Table 17.
Address
Register name
Function
0x301000
WD_PROTECT WDT Write Protect Register
Enable WDT register write protection
0x301002
WD_EN
WDT Enable and Setup Register
Configure and start watchdog timer
0x301004
WD_CMP_L
WDT Comparison Data L Register
Comparison data
0x301006
WD_CMP_H
WDT Comparison Data H Register
0x301008
WD_CNT_L
WDT Count Data L Register
Watchdog timer counter data
0x30100a
WD_CNT_H
WDT Count Data H Register
0x30100c
WD_CTL
WDT Control Register
Reset watchdog timer
The following describes each WDT register. These are all 16-bit registers.
Notes: • When data is written to the registers, the “Reserved” bits must always be written as 0 and not 1.
• The WD_PROTECT register (0x301000) allows 16-bit access only. Other registers (0x301002
to 0x30100c) allow 8-bit access as well as 16-bit access.
WDT Write Protect Register (WD_PROTECT)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
WDT
Write Protect
Register
(WD_
PROTECT)
0x301000
(16 bits)
D15–0 WDPTC
[15:0]
WDT register write protect flag
Writing 0x96 removes the write
protection of the WD_EN, WD_
CMP_L, and WD_CMP_H reg-
isters (0x301002–0x301006).
Writing another value set the
write protection.
X
W 0 when being read.
D[15:0] WDPTC[15:0]: WDT Register Write Protect Flag Bits
These bits set or clear write protection at addresses 0x301002 to 0x301006.
0x96 (W):
Clears write protection
Other than 0x96 (W): Applies write protection (default, indeterminate value)
0x0 (R):
Always 0x0 when read
Before altering the WDT_EN, WDT_CMP_L, or WDT_CMP_H register, write 0x96 to WDPTC[15:0]
to remove write protection. Setting WDPTC[15:0] to other than 0x96 will result in the contents of
the registers above not being altered even when executing the write instruction without any problem.
Once write protection is removed by writing 0x96 to WDPTC[15:0], said registers can be rewritten any
number of times until WDPTC[15:0] is set to other than 0x96. When the WDT_EN, WDT_CMP_L, or
WDT_CMP_H have been rewritten, be sure to write other than 0x96 to WDPTC[15:0] to prevent erro-
neous writing to the registers.