UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
134 of 362
NXP Semiconductors
UM10208
Chapter 11: LPC2800 WDT
4.8 Watchdog External Match Register (WDT_EMR - 0x8000 283C)
If the Watchdog interrupt or reset function is used, this register must be programmed to
signal the Event Router or CGU when a TC match occurs.
5.
Sample setup
The following table shows how registers in the Watchdog Timer, Clock Generation Unit,
and Event Router can be programmed to request an interrupt if the WDT is not cleared by
software within 65,536 WDT clocks, and to reset the LPC288x if the WDT is not cleared
by software for 131,072 clocks. The order of the table entries is the recommended order in
which the registers should be programmed.
Table 137: Watchdog External Match Register (WDT_EMR - 0x8000 283C)
Bit
Function
Description
Reset Value
0
m0
This read-only bit reflects the state of the m0 output that is sent
to the Event Router.
0
3:1
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-
5:4
Enable
Interrupt
This field controls how a match between TC and MR0 affects
the m0 output that is sent to the Event Router:
0x: disable the Watchdog Interrupt function
10: enable the Watchdog Interrupt function
11: do not use
00
6
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-
7
Enable
Reset
This bit controls whether a match between TC and MR1 affects
the m1 output that is routed to the CGU:
0: disable the Watchdog Reset function
1: enable the Watchdog Reset function
0
31:8 -
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-
Table 138. Sample setup
Module
Register
Value
Result
WDT
WDT_TCR
0x0002 Clear and disable TC
WDT_PR
0x0003 Prescaler = 4 clocks
WDT_MR0
0x4000 Interrupt at 4
×
0x4000 = 65,536 processor clocks
WDT_MR1
0x8000 Reset at 4
×
0x8000 = 131,072 processor clocks
WDT_MCR
0x0001 Enable status bit for interrupt
WDT_ECR
0x00A0 Drive m0 and m1 high on match
CGU
WDT_ESR
3
Use APB0 fractional divider 1
CGU
WDT_PCR
7
(reset value, need not be programmed)