7549 datasheet(46/84 Pages) RENESAS

46 / 84 page

Rev.2.01

Oct 15, 2007

Page 46 of 81

REJ03B0202-0201

7549 Group

Clock Generating Circuit

The clock generating circuit includes the XIN clock (ceramic

oscillator or crystal oscillator can be used), XCIN clock (32 kHz

oscillator can be used), external clock input, high-speed on-chip

oscillator, and low-speed on-chip oscillator.

Pins P20/XOUT/XCOUT and P21/XIN/XCIN can be shared for the

ports, XIN oscillation, and XCIN oscillation.

Use the oscillation method selection bits (bits 1 and bit 0 in

function set ROM data 1 (FSROM1)) to set the function of these

pins.

• Ceramic Resonator or Crystal Oscillator

Set the oscillation method selection bits (bits 1 and bit 0 in

FSROM1) to “012”, and connect the ceramic resonator (or the

oscillator) and external circuit with the shortest wiring length

possible.

The constants of the oscillator circuit differ depending on the

resonator. Use the values recommended by the resonator

manufacturer. (An external feedback resistor may be necessary

under some conditions.)

Setting the XIN/XCIN oscillation control bit to “0” starts

oscillation. This bit is sets to “0” after reset.

• 32 kHz Crystal Oscillator

Set the oscillation method selection bits to “102”, and connect the

32 kHz crystal oscillator and external circuit with the shortest

wiring length possible.

The constants of the oscillator circuit differ depending on the

resonator. Use the values recommended by the resonator

manufacturer. (An external feedback resistor may be necessary

under some conditions.)

Setting the XIN/XCIN oscillation control bit to “0” starts

oscillation. This bit is sets to “0” after reset.

• External Clock Input

Set the oscillation method selection bits to “112”, and connect the

clock source to the P20/XOUT pin. In this case, the P21/XIN pin

can be used as an I/O port.

• High-Speed On-Chip Oscillator

The high-speed on-chip oscillator is stopped after reset.

Setting the high-speed on-chip oscillator oscillation control bit

(bit 1 in CLKM) to “0” starts oscillation. This bit is sets to “1”

after reset.

• Low-Speed On-Chip Oscillator

The low-speed on-chip oscillator automatically starts oscillating

after reset.

Setting the low-speed on-chip oscillator oscillation control bit

(bit 0 in CLKM) to “1” stops oscillation. This bit is sets to “0”

after reset. If the low-speed on-chip oscillator control bit (bit 4 in

FSROM2) is set to “0” and stopping the low-speed on-chip

oscillator is disabled, the low-speed on-chip oscillator oscillation

control bit cannot be set to “1” and oscillation cannot be stopped.

Also, the oscillator does not stop even when the STP instruction

is executed.

• Using No Oscillator Pins (P20 as output port and P21

as I/O port)

To use only an internal on-chip oscillator, set the oscillation

method selection bits to “002”. The P20/XOUT pin can be used as

an output port and the P21/XIN pin can be used as an I/O port.

Fig 60. Structure of function set ROM data 1

Fig 61. External circuit of ceramic resonator

Fig 62. External circuit of 32 kHz quarts-crystal

oscillator

Fig 63. External clock input circuit

Oscillation method select bits (Note 1)

b1 b0

0 0: No resonator used (P20 and P21 set as I/O ports)

0 1: Ceramic resonator or quartz-crystal oscillation

1 0: 32 kHz quartz-crystal oscillation

1 1: External clock input (P21 set as I/O port)

Stop mode low voltage detection circuit enable/disable bit

(Note 2)

0: Low voltage detection circuit disabled in stop mode

1: Low voltage detection circuit enabled in stop mode

Always set these bits to 0.

Always set this bit to 1.

Function set ROM data 1

FSROM1 (FFD916)

Notes 1: The P20/XOUT and P21/XIN pins build in an on-chip oscillator. Even if these

pins are used as I/O ports, the oscillator circuit is enabled when the MCU’s Vcc

voltage drops below the operation limit voltage. In this case these pins may output

undefined values.

2: If the low voltage detection circuit is enabled in stop mode, power consumption in

stop mode will increase.

M37549

XIN

XOUT

COUT

CIN

Insert a damping resistor if required.

The resistance will vary depending

on the oscillator and the oscillation

drive capacity setting.

Use the value recommended by the

maker of the oscillator.

Also, if the oscillator manufacturer’s

data sheet specifies that a feedback

resistor be added external to the chip

though a feedback resistor exists on-

chip, insert a feedback resistor

between XIN and XOUT following the

instruction.

M37549

XCIN

XCOUT

CCOUT

C CIN

Insert a damping resistor if required.

The resistance will vary depending

on the oscillator and the oscillation

drive capacity setting.

Use the value recommended by the

maker of the oscillator.

Also, if the oscillator manufacturer’s

data sheet specifies that a feedback

resistor be added external to the

chip though a feedback resistor

exists on-chip, insert a feedback

resistor between XIN and XOUT

following the instruction.

M37549

P21

XOUT

I/O port

External

oscillation circuit

Vcc

Vss

Connect the external clock

to the P20/XOUT pin, not

the P21/XIN pin.

7549 Datasheet(PDF) 46 Page - Renesas Technology Corp

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