General Overview; Watchdog Timer Operation; Timing Specifications; Figure 14-1 Watchdog Timer Functional Block Diagram - Motorola DragonBall MC9328MX1 Reference Manual

Chapter 14
Watchdog Timer Module

14.1 General Overview

The watchdog timer module of the MC9328MX1 protects against system failures by providing a method of
escaping from unexpected events or programming errors. Once activated, the timer must be serviced by
software on a periodic basis. If servicing does not take place, the timer times out. Upon a time-out, the
watchdog timer module either asserts a system reset signal WDT_RST or a interrupt request signal
WDT_INT depending on software configuration. Table 14-1 on page 14-5 shows the watchdog timer
module's input and output signals. A state machine that demonstrates the time-out operation of the counter
operation is shown in Figure 14-2 on page 14-4.

14.2 Watchdog Timer Operation

The following sections describe the operation and programming of the watchdog timer module.

14.2.1 Timing Specifications

The watchdog timer provides time-out periods from 0.5 seconds up to 64 seconds with a time resolution of
0.5 seconds. As shown in Figure 14-1, the watchdog timer uses the CLK2HZ clock (from RTC module) as
an input to achieve the resolution of 0.5 seconds and a frequency of 2 Hz. This clock is connected to the
input of a 7-bit counter to obtain a range of 0.5 to 64 seconds. The user can determine the time-out period
by writing to the watchdog time-out field (WT[6:0]) in the Watchdog Control Register (WCR).
WHALT
WDE
(Time-Out)
7-bit Counter
CLK2HZ
0
CLK32K
1
Test Mode (TMD bit)
Figure 14-1. Watchdog Timer Functional Block Diagram
MOTOROLA Watchdog Timer Module 14-1