UM10346_1
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 01 — 2 November 2009
100 of 132
NXP Semiconductors
UM10346
LPC980/982 User manual
PRE is the value of prescaler (PRE2 to PRE0) which can be the range 0 to 7, and;
WDL is the value of watchdog load register which can be the range of 0 to 255.
The minimum number of tclks is:
(3)
The maximum number of tclks is:
(4)
shows sample P89LPC980/982 timeout values.
tclks
2
5
0
+
(
)
(
)
0
1
+
(
)
1
33
=
+
=
tclks
2
5
7
+
(
)
(
)
255
1
+
(
)
1
1048577
=
+
=
Table 87.
Watchdog Timer Control register (WDCON - address A7h) bit allocation
Bit
7
6
5
4
3
2
1
0
Symbol
PRE2
PRE1
PRE0
-
-
WDRUN
WDTOF
WDCLK
Reset
1
1
1
x
x
1
1/0
1
Table 88.
Watchdog Timer Control register (WDCON - address A7h) bit description
Bit Symbol
Description
0
WDCLK
Watchdog input clock select. When set, the watchdog oscillator is selected. When cleared, PCLK is
selected. (If the CPU is powered down, the watchdog is disabled if WDCLK = 0, see
both WDTE and WDSE are set to 1, this bit is forced to 1.) Refer to
for details.
1
WDTOF
Watchdog Timer Time-Out Flag. This bit is set when the 8-bit down counter underflows. In watchdog mode,
a feed sequence will clear this bit. It can also be cleared by writing a logic 0 to this bit in software.
2
WDRUN Watchdog Run Control. The watchdog timer is started when WDRUN = 1 and stopped when WDRUN = 0.
This bit is forced to 1 (watchdog running) and cannot be cleared to zero if both WDTE and WDSE are set to
1.
3:4 -
reserved
5
PRE0
Clock Prescaler Tap Select. Refer to
for details.
6
PRE1
7
PRE2
Table 89.
Watchdog timeout vales (designer check)
PRE2 to PRE0 WDL in
decimal)
Timeout Period
(in watchdog
clock cycles)
Watchdog Clock Source
25 KHz Watchdog
Oscillator Clock
(Nominal)
400 KHz Watchdog
Oscillator Clock
(Nominal)
12 MHz CCLK
(6 MHz
CCLK
⁄
2
Watchdog Clock)
000
0
33
1.32 ms
82.5
μ
s
5.50
μ
s
255
8,193
328.0 ms
20.5 ms
1.37 ms
001
0
65
2.6 ms
162.5
μ
s
10.8
μ
s
255
16,385
656.0 ms
41.0 ms
2.73 ms
010
0
129
5.16
μ
s
322.5
μ
s
21.5
μ
s
255
32,769
1.31 s
81.9 ms
5.46 ms
011
0
257
10.28 ms
642.5
μ
s
42.8
μ
s
255
65,537
2.62 s
163.8 ms
10.9 ms