R8C/20 Group, R8C/21 Group 14. Timers
Rev.2.00 Aug 27, 2008 Page 147 of 458
REJ09B0250-0200
14.2.3 Programmable One-shot Generation Mode
Programmable one-shot generation mode is mode to output the one-shot pulse from the TRBO pin by a
program or an external trigger input (input to the INT0
pin) (see Table 14.9 Programmable One-Shot
Generation Mode Specifications). When a trigger is generated, the timer starts operating from the point only
once for a given period equal to the set value in the TRBPR register. The TRBSC register is unused in this
mode.
Figure 14.21 shows the TRBIOC Register in Programmable One-Shot Generation Mode. Figure 14.22 shows
the Operation Example of Programmable One-Shot Generation Mode.
NOTES:
1. The set value is reflected at the following one-shot pulse after writing to the TRBPR register.
2. Do not set both the TRBPRE and TRBPR registers to 00h.
Table 14.9 Programmable One-Shot Generation Mode Specifications
Item Specification
Count Sources f1, f2, f8, timer RA underflow
Count Operations • Decrement the setting value in the TRBPR register
• When the timer underflows, it reloads the contents of the reload register before
the count completes and the TOSSTF bit is set to 0 (one-shot stops).
• When a count stops, the timer reloads the contents of the reload register before
it stops.
One-Shot Pulse
Output Time
(n+1)(m+1)/fi
fi: Count source frequency,
n: Setting value in TRBPRE register, m: Setting value in TRBPR register
(2)
Count Start
Conditions
• The TSTART bit in the TRBCR register is set to 1 (count starts) and the next
trigger is generated.
• Set the TOSST bit in the TRBOCR register to 1 (one-shot starts)
• Input trigger to the INT0
pin
Count Stop
Conditions
• When reloading completes after Timer RB underflows during primary period.
• When the TOSSP bit in the TRBOCR register is set to 1 (one-shot stops)
• When the TSTART bit in the TRBCR register is set to 0 (stops counting)
• When the TSTOP bit in the TRBCR register is set to 1 (forcibly stops counting)
Interrupt Request
Generation Timing
In half cycles of count source, after the timer underflows (at the same time as the
TRBO output ends) [timer RB interrupt]
TRBO Pin Function Pulse output
INT0
Pin Functions • When the INOSTG bit in the TRBIOC register is set to 0 (INT0 one-shot trigger
disabled), programmable I/O port or INT0
interrupt input
• When the INOSTG bit in the TRBIOC register is set to 1 (INT0
one-shot trigger
enabled), external trigger (INT0
interrupt input)
Read from Timer The count value can be read out by reading the TRBPR and TRBPRE registers.
Write to Timer • When registers TRBPRE and TRBPR are written while the count is stopped,
values are written to both the reload register and counter.
• When registers TRBPRE and TRBPR are written during the count, values are
written to the reload register only (the data is transferred to the counter at the
following reload)
(1)
Select Functions • Output level select function
The TOPL bit in the TRBIOC register can select the output level of the one-shot
pulse waveform.
• One-shot trigger select function
Refer to 14.2.3.1 One-Shot Trigger Selection.
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