R8C28 datasheet(93/473 Pages) RENESAS

93 / 473 page

R8C/28 Group, R8C/29 Group

10. Clock Generation Circuit

Rev.2.10

Sep 26, 2008

Page 74 of 441

REJ09B0279-0210

Figure 10.2

CM0 Register

System Clock Control Register 0

(1)

Symbol

Address

After Reset

CM0

0006h

01101000b

Bit Symbol

Bit Name

Function

NOTES:

10.

11.

12. For J, K version, the XCIN clock oscillation circuit cannot be used. Do not set to 1.

b7 b6 b5 b4 b3 b2 b1 b0

—

(b0)

Reserved bit

Set to 0.

CM02

WAIT peripheral function clock

stop bit

0 : Peripheral function clock does not stop

in w ait mode

1 : Peripheral function clock stops in w ait

mode

CM01

XIN-XCIN sw itch bit(12)

0 : XIN clock

1 : XCIN clock

CM03

XCIN-XCOUT drive capacity

select bit(2)

0 : Low

1 : High

CM04

XCIN clock (XCIN-XCOUT)

oscillate bit(3, 4, 5, 12)

0 : XCIN clock stops

1 : XCIN clock oscillates(6, 7)

CM05

XIN clock (XIN-XOUT)

stop bit(3, 8)

0 : XIN clock oscillates(9)

1 : XIN clock stops(10)

CM06

System clock division select bit

0(11)

0 : CM16, CM17 enabled

1 : Divide-by-8 mode

During external clock input, only the clock oscillation buffer is turned off and clock input is acknow ledged.

When entering stop mode, the CM06 bit is set to 1 (divide-by-8 mode).

P4_6 and P4_7 can be used as input ports w hen the CM04 bit is set to 0 (XCIN clock stops), the CM05 bit is set to 1

(XIN clock stops) and the CM13 bit in the CM1 register is set to 0 (P4_6, P4_7).

To use the XCIN clock, set the CM04 bit to 1. Also, set ports P4_6 and P4_7 as input ports w ithout pull-up.

Set the CM01 bit to 1 (XCIN clock).

The CM05 bit stops the XIN clock w hen the high-speed on-chip oscillator mode, low -speed on-chip oscillator mode is

selected. Do not use this bit to detect w hether the XIN clock is stopped. To stop the XIN clock, set the bits in the

follow ing order:

(a) Set bits OCD1 to OCD0 in the OCD register to 00b.

(b) Set the OCD2 bit to 1 (selects on-chip oscillator clock).

Set the PRC0 bit in the PRCR register to 1 (w rite enable) before rew riting the CM0 register.

Set the CM01 bit to 0 (XIN clock).

The MCU enters stop mode, the CM03 bit is set to 1 (high). Rew rite the CM03 bit w hile the XCIN clock oscillation

stabilizes.

The CM04 bit can be set to 1 by a program but cannot be set to 0.

When the CM10 bit is set to 1 (stop mode) and the CM04 bit is set to 1 (XCIN clock oscillates), the XCOUT (P4_7) pin

goes “H”.

When the CM04 bit is set to 0 (XCIN clock stops), P4_7 (XCOUT) enters input mode.

—

(b7)

Reserved bit

Set to 0.

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