7540 datasheet(13/88 Pages) RENESAS

13 / 88 page

7540 Group

Rev.4.00

Jun 21, 2004

page 13 of 82

REJ03B0011-0400Z

[CPU mode register] CPUM

The CPU mode register contains the stack page selection bit.

This register is allocated at address 003B16.

Switching method of CPU mode register

Switch the CPU mode register (CPUM) at the head of program af-

ter releasing Reset in the following method.

Fig. 12 Switching method of CPU mode register

Fig. 11 Structure of CPU mode register

Oscillation mode selection bit (Note 1)

0 : Ceramic oscillation

1 : RC oscillation

CPU mode register

(CPUM: address 003B16, initial value: 8016)

Stack page selection bit

0 : 0 page

1 : 1 page

Clock division ratio selection bits

b7 b6

0 : f(

φ) = f(XIN)/2 (High-speed mode)

1 : f(

φ) = f(XIN)/8 (Middle-speed mode)

0 : applied from on-cihp oscillator

1 : f(

φ) = f(XIN) (Double-speed mode)(Note 2)

On-chip oscillator oscillation control bit

0 : On-chip oscillator oscillation enabled

1 : On-chip oscillator oscillation stop

XIN oscillation control bit

0 : Ceramic or RC oscillation enabled

1 : Ceramic or RC oscillation stop

Processor mode bits (Note 1)

b1 b0

0 Single-chip mode

Not available

2: These bits are used only when a ceramic oscillation is selected.

Note 1: The bit can be rewritten only once after releasing reset. After rewriting

it is disable to write any data to the bit. However, by reset the bit is

initialized and can be rewritten, again.

(It is not disable to write any data to the bit for emulator MCU

“M37540RSS”.)

Do not use these when an RC oscillation is selected.

After releasing reset

Switch the oscillation mode

selection bit (bit 5 of CPUM)

Switch the clock division ratio

selection bits (bits 6 and 7 of CPUM)

Main routine

Start with an on-chip oscillator

An initial value is set as a ceramic

oscillation mode. When it is switched to an

RC oscillation, its oscillation starts.

Select 1/1, 1/2, 1/8 or on-chip oscillator.

Wait by on-chip oscillator operation

until establishment of oscillator clock

When using a ceramic oscillation, wait until

establlishment of oscillation from oscillation starts.

When using an RC oscillation, wait time is not required

basically (time to execute the instruction to switch from

an on-chip oscillator meets the requirement).

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