R8C2K datasheet(446/471 Pages) RENESAS

446 / 471 page

R8C/2K Group, R8C/2L Group

23. Usage Notes

Rev.1.10

Dec 21, 2007

Page 429 of 450

REJ09B0406-0110

23.3.2.2

Programmable waveform generation mode

The following three workarounds should be performed in programmable waveform generation mode.

(1) To write to registers TRBPRE and TRBPR during count operation (TCSTF bit is set to 1), note the

following points:

• When the TRBPRE register is written continuously, allow three or more cycles of the count source for each

write interval.

• When the TRBPR register is written continuously, allow three or more cycles of the prescaler underflow for

each write interval.

(2) To change registers TRBPRE and TRBPR during count operation (TCSTF bit is set to 1), synchronize the

TRBO output cycle using a timer RB interrupt, etc. This operation should be preformed only once in the

same output cycle. Also, make sure that writing to the TRBPR register does not occur during period A

shown in Figures 23.2 and 23.3.

The following shows the detailed workaround examples.

• Workaround example (a):

As shown in Figure 23.2, write to registers TRBSC and TRBPR in the timer RB interrupt routine. These write

operations must be completed by the beginning of period A.

Figure 23.2

Workaround Example (a) When Timer RB interrupt is Used

TRBO pin output

Count source/

prescaler

underflow signal

Primary period

Period A

IR bit in

TRBIC register

Secondary period

(b)

Interrupt

sequence

Instruction in

interrupt routine

Interrupt request is

acknowledged

(a)

Interrupt request

is generated

Ensure sufficient time

Set the secondary and then

the primary register immediately

(a) Period between interrupt request generation and the completion of execution of an instruction. The length of time

varies depending on the instruction being executed.

The DIVX instruction requires the longest time, 30 cycles (assuming no wait states and that a register is set as

the divisor).

(b) 20 cycles. 21 cycles for address match and single-step interrupts.

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