R8C/20 Group, R8C/21 Group 14. Timers
Rev.2.00 Aug 27, 2008 Page 144 of 458
REJ09B0250-0200
14.2.2 Programmable Waveform Generation Mode
Programmable waveform generation mode is mode to invert the signal output from the TRBO pin each time the
counter underflows, while the values in the TRBPR and TRBSC registers are counted alternately (see Table
14.8 Programmable Waveform Generation Mode Specifications). A counting starts by counting the setting
value in the TRBPR register. The TRBOCR register is unused in this mode.
Figure 14.19 shows the TRBIOC Register in Programmable Waveform Generation Mode. Figure 14.20 shows
the Operation Example of Timer RB in Programmable Waveform Generation Mode.
NOTES:
1. Even when counting the secondary period, read out the TRBPR register.
2. The set values are reflected to the waveform output beginning with the following primary period after
writing to the TRBPR register.
3. The value written to the TOCNT bit is enabled by the following.
• When count starts.
• When the timer RB interrupt request is generated.
The contents after the TOCNT bit is changed are reflected from the output of the following
primary period.
Table 14.8 Programmable Waveform Generation Mode Specifications
Item Specification
Count Sources
f1, f2, f8, timer RA underflow
Count Operations • Decrement
• When the timer underflows, it reloads the contents of the primary reload and
secondary reload registers alternately before the count continues.
Width and Period of
Output Waveform
Primary period: (n+1)(m+1)/fi
Secondary period: (n+1)(p+1)/fi
Period: (n+1){(m+1)+(p+1)}/fi
fi: Count source frequency
n: Setting value in TRBPRE register
m: Setting value in TRBPR register
p: Setting value in TRBSC register
Count Start Condition Write 1 (count start) to the TSTART bit in the TRBCR register
Count Stop
Conditions
• Write 0 (count stop) to the TSTART bit in the TRBCR register
• Write 1 (count forcibly stop) to the TSTOP bit in the TRBCR register
Interrupt Request
Generation Timing
In half of count source, after timer RB underflows during secondary period (at the
same time as the TRBO output change) [timer RB interrupt]
TRBO Pin Function Programmable output port or pulse output
INT0
Pin Function Programmable I/O port or INT0 interrupt input
Read from Timer
The count value can be read out by reading the TRBPR and TRBPRE registers
(1)
Write to Timer • When registers TRBPRE, TRBSC, and TRBPR are written while the count is
stopped, values are written to both the reload register and counter.
• When registers TRBPRE, TRBSC, and TRBPR are written to during count
operation, values are written to the reload registers only.
(2)
Select Functions • Output level select function
The TOPL bit can select the output level during primary and secondary periods.
• TRBO pin output switch function
Timer RB pulse output or P3_1 latch output is selected by the TOCNT bit in the
TRBIOC register.
(3)
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