NXP Semiconductors P89LPC9321 UM10310 - Manual (Page 101)

UM10310 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
User manual Rev. 2 — 1 November 2010 101 of 139
NXP Semiconductors
UM10310
P89LPC9321 User manual
[1] The Keypad Interrupt must be enabled in order for the settings of the KBMASK register to be effective.
15. Watchdog timer (WDT)
The watchdog timer subsystem protects the system from incorrect code execution by
causing a system reset when it underflows as a result of a failure of software to feed the
timer prior to the timer reaching its terminal count. The watchdog timer can only be reset
by a power-on reset.
15.1 Watchdog function
The user has the ability using the WDCON, CLKCON and UCFG1 registers to control the
run /stop condition of the WDT, the clock source for the WDT, the prescaler value, and
whether the WDT is enabled to reset the device on underflow. In addition, there is a safety
mechanism which forces the WDT to be enabled by values programmed into UCFG1
either through IAP or a commercial programmer.
The WDTE bit (UCFG1.7), if set, enables the WDT to reset the device on underflow.
Following reset, the WDT will be running regardless of the state of the WDTE bit.
The WDRUN bit (WDCON.2) can be set to start the WDT and cleared to stop the WDT.
Following reset this bit will be set and the WDT will be running. All writes to WDCON need
to be followed by a feed sequence (see
Section 15.2 ). Additional bits in WDCON allow the
user to select the clock source for the WDT and the prescaler.
When the timer is not enabled to reset the device on underflow, the WDT can be used in
‘timer mode’ and be enabled to produce an interrupt (IEN0.6) if desired.
The Watchdog Safety Enable bit, WDSE (UCFG1.4) along with WDTE, is designed to
force certain operating conditions at power-up. Refer to
Table 96 for details.
Figure 51 shows the watchdog timer in watchdog mode. It consists of a programmable
13-bit prescaler, and an 8-bit down counter. The down counter is clocked (decremented)
by a tap taken from the prescaler. The clock source for the prescaler is either PCLK, low
Table 94. Keypad Interrupt Mask register (KBMASK - address 86h) bit allocation
Bit 7 6 5 4 3 2 1 0
Symbol KBMASK.7 KBMASK.6 KBMASK.5 KBMASK.4 KBMASK.3 KBMASK.2 KBMASK.1 KBMASK.0
Reset 0 0 0 0 0 0 0 0
Table 95. Keypad Interrupt Mask register (KBMASK - address 86h) bit description
Bit Symbol Description
0 KBMASK.0 When set, enables P0.0 as a cause of a Keypad Interrupt.
1 KBMASK.1 When set, enables P0.1 as a cause of a Keypad Interrupt.
2 KBMASK.2 When set, enables P0.2 as a cause of a Keypad Interrupt.
3 KBMASK.3 When set, enables P0.3 as a cause of a Keypad Interrupt.
4 KBMASK.4 When set, enables P0.4 as a cause of a Keypad Interrupt.
5 KBMASK.5 When set, enables P0.5 as a cause of a Keypad Interrupt.
6 KBMASK.6 When set, enables P0.6 as a cause of a Keypad Interrupt.
7 KBMASK.7 When set, enables P0.7 as a cause of a Keypad Interrupt.