HD404356 Datasheet, PDF (54/100 Pages) Hitachi Semiconductor – 4-bit HMCS400-Series microcomputer

HD404358 Series
Timer C Operations:
• Free-running/reload timer operation: The free-running/reload operation, input clock source, and
prescaler division ratio are selected by timer mode register C (TMC: $00D).
Timer C is initialized to the value set in timer write register C (TWCL: $00E, TWCU: $00F) by
software and incremented by one at each clock input. If an input clock is applied to timer C after it has
reached $FF, an overflow is generated. In this case, if the reload timer function is enabled, timer C is
initialized to its initial value set in timer write register C; if the free-running timer function is enabled,
the timer is initialized to $00 and then incremented again.
The overflow sets the timer C interrupt request flag (IFTC: $002, bit 2). IFTC is reset by software or
MCU reset. Refer to figure 3 and table 1 for details.
• Watchdog timer operation: Timer C is used as a watchdog timer for detecting out-of-control program
routines by setting the watchdog on flag (WDON: $020, bit 1) to 1. If a program routine runs out of
control and an overflow is generated, the MCU is reset. The watchdog timer operation flowchart is
shown in figure 41. Program run can be controlled by initializing timer C by software before it reaches
$FF.
$FF + 1
Timer C
count value
$00
Overflow
Time
CPU
operation
Normal Timer C Normal Timer C
operation clear operation clear
Program
runaway
Reset
Normal
operation
Figure 41 Watchdog Timer Operation Flowchart
• Timer output operation: The PWM output modes can be selected for timer C by setting port mode
register A (PMRA: $004).
By selecting the timer output mode, pin R0₃/TOC is set to TOC. The output from TOC is reset low by
MCU reset.
PWM output: When PWM output mode is selected, timer C provides the variable-duty pulse output
function. The output waveform differs depending on the contents of timer mode register C (TMC:
$00D) and timer write register C (TWCL: $00E, TWCU: $00F). The output waveform is shown in
figure 42.
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