III PERIPHERAL BLOCK: 16-BIT PROGRAMMABLE TIMERS
Uses of 16-Bit Programmable Timers
The up-counters of the 16-bit programmable timer cyclically output a comparison-match signal in accordance with the comparison data that are set in the software. This signal is used to generate an interrupt request to the CPU or control the internal peripheral circuits. A clock generated from the signal can also be output to external devices.
CPU interrupt request/IDMA invocation request
Each timer's comparison match (matching of counter and comparison data) can be used as an interrupt factor to generate an interrupt request to the CPU. Therefore, an interrupt can be generated at an interval that is set in the software.
Furthermore, this interrupt factor can also be used to invoke IDMA or HSDMA.
Clock output to external devices
A clock generated from the comparison-match signal can be output from the chip to the outside. The clock cycle is determined by comparison data B, and the duty ratio is determined by comparison data A. This output can be used to control external devices. The output pins of each timer are described in the preceding section.
A/D converter start trigger
The A/D converter allows a trigger to start the A/D conversion to be selected from among four available types. One is the comparison-match B of the 16-bit programmable timer 0. This makes it possible to perform the A/D conversion at programmable intervals.
To use this function, write "01" to the A/D converter control TS[1:0] (D[4:3]) / A/D trigger register (0x40242) to select the 16-bit programmable timer 0 as the trigger.
Watchdog timer
The 16-bit programmable timer 0 can be used as a watchdog timer to monitor CPU crash. In this case, the comparison-match B of this timer serves as an NMI request signal to the CPU.
To use this function, write "1" to the watchdog timer control bit EWD (D1) / Watchdog timer enable register (0x40171) to enable the NMI. For details on how to control the watchdog timer, refer to "Watchdog Timer".
