M37544 Datasheet, PDF (12/68 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

7544 Group
[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.
b7
b0
CPU mode register
(CPUM: address 003B16, initial value: 8016)
Processor mode bits (Note 1)
b1 b0
0 0 Single-chip mode
0 1 _{Not available}
10
11
Stack page selection bit
0 : 0 page
1 : 1 page
On-chip oscillator oscillation control bit
0 : On-chip oscillator oscillation enabled
1 : On-chip oscillator oscillation stop
XIN oscillation control bit
0 : Ceramic/quartz-crystal or RC oscillation enabled
1 : Ceramic/quartz-crystal or RC oscillation stop
Oscillation mode selection bit (Note 1)
0 : Ceramic/quartz-crystal oscillation
1 : RC oscillation
Clock division ratio selection bits
b7 b6
0 0 : f(φ) = f(XIN)/2 (High-speed mode)
0 1 : f(φ) = f(XIN)/8 (Middle-speed mode)
1 0 : applied from on-chip oscillator
1 1 : f(φ) = f(XIN) (Double-speed mode)(Note 2)
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
“M37544RSS”.)
2: These bits are used only when a ceramic/quartz-crystal oscillation is selected.
Do not use these when an RC oscillation is selected.
Fig. 11 Structure of CPU mode register
After releasing reset
Start with an on-chip oscillator
Switch the oscillation mode
selection bit (bit 5 of CPUM)
An initial value is set as a ceramic/quartz-crystal
oscillation mode. When it is switched to an RC
oscillation, its oscillation starts.
Wait by on-chip oscillator operation
until establishment of oscillator clock
When using a ceramic/quartz-crystal 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).
Switch the clock division ratio
Select 1/1, 1/2, 1/8 or on-chip oscillator.
selection bits (bits 6 and 7 of CPUM)
Main routine
Fig. 12 Switching method of CPU mode register
Rev.1.04 2004.06.08 page 12 of 66
REJ03B0012-0104Z