R8CSLASH20 datasheet(151/501 Pages) RENESAS

151 / 501 page

R8C/20 Group, R8C/21 Group

14. Timers

Rev.2.00 Aug 27, 2008

Page 135 of 458

REJ09B0250-0200

Figure 14.12

Operating Example of Pulse Period Measurement Mode

Underflow signal of timer

RA prescaler

NOTES:

1. The contents of the read-out buffer can be read when the TRA register is read in pulse period measurement mode.

2. After an active edge of measurement pulse is input, the TEDGF bit in the TRACR register is set to 1 (active edge found) when the timer RA

prescaler underflows for the second time.

3. The TRA register should be read before the next active edge is input after the TEDGF bit is set to 1 (active edge found).

The content in the read-out buffer is retained until the TRA register is read. If the TRA register is not read before the next active edge is

input, the measured result of the previous period is retained.

4. When set to 0 by a program, use a MOV instruction to write 0 to the TEDGF bit in the TRACR register. At the same time, write 1 to the

TUNDF bit in the TRACR register.

5. When set to 0 by a program, use a MOV instruction to write 0 to the TUNDF bit. At the same time, write 1 to the TEDGF bit.

6. The TUNDF and TEDGF bits are both set to 1 if the timer RA underflows and reloads on an active edge simultaneously.

0Eh 0Dh 0Fh 0Eh 0Dh 0Ch 0Bh 0Ah 09h 0Fh 0Eh 0Dh

01h 00h 0Fh 0Eh

0Fh

0Dh

0Fh

0Bh 0Ah

0Dh

01h 00h 0Fh 0Eh

09h

TSTART bit in

TRACR register

TEDGF bit in

TRACR register

Measurement pulse

(TRAIO pin input)

Contents of TRA

Contents of read-out

buffer(1)

IR bit in TRAIC

TUNDF bit in

TRACR register

Set to 1 by program

Starts counting

TRA reloads

TRA read(3)

Retained

(4)

(2)

Set to 0 by program

(5)

(6)

Conditions: A period from one rising edge to the next rising edge of measurement pulse is measured (TEDGSEL = 0) with

the default value of the TRA register as 0Fh.

0Eh

TRA reloads

Retained

Set to 0 when interrupt request is acknowledged, or set by program

Set to 0 by program

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