HD404669 Datasheet, PDF (62/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 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 C1 (TMC1: $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 (TWCL: $00E, TWCU: $00F); 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 ). The timer C interrupt request flag
is reset by the program, an MCU reset or a transition to stop mode. For details, see figure 3, Configuration
of Interrupt Control Bits and Register Flag Area, and table 1, Initial Values after MCU Reset.
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. Program run can be controlled by initializing timer C by
software before it reaches $FF.
Timer output operation: The following four output modes can be selected for timer C by setting timer
mode register C2 (TMC2: $014). With timer C, the R3₁/TOC pin is designated as the TOC pin, and toggle
waveform output, low-level output, high-level output, or PWM waveform output can be selected, by timer
mode register C2 (TMC2: $014). TOC pin output is initialized to the low level by an MCU reset.
• Toggle output
With toggle output, the output level is changed upon input of the next clock pulse after the timer C
value reaches $FF. Use of this function in combination with the reload timer allows a clock signal with
any period to be output, enabling it to be used as buzzer output. The output waveform is shown in
figure 42.
• Low-level output
With low-level output, the output is changed to the low level when timer C overflows. This function
should be used when the output is high.
• High-level output
With high-level output, the output is changed to the high level when timer C overflows. This function
should be used when the output is low.
• PWM output
With PWM output, variable-duty pulses are output. The output waveform is as shown in figure 42,
according to the contents of timer mode register C1 (TMC1: $00D) and timer write register C (TWCL:
$00E, TWCU: $00F).
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