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7531 Group User’s Manual
1-13
HARDWARE
[CPU Mode Register] CPUM
The CPU mode register contains the stack page selection bit.
This register is allocated at address 003B16.
Fig. 12 Switching method of CPU mode register
Switching method of CPU mode register
Switch the CPU mode register (CPUM) at the head of program after
releasing Reset in the following method.
Fig. 11 Structure of CPU mode register
Oscillation mode selection bit (Note 1)
0 : Ceramic oscillation
1 : RC oscillation
CPU mode register
(CPUM: address 003B 16, initial value: 80 16)
Stack page selection bit
0 : 0 page
1 : 1 page
C
lock 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 ring oscillator
1
1 : f(
φ) = f(XIN) (Double-speed mode)(Note 2)
Not used (returns “0” when read)
(Do not write “1” to these bits )
Processor mode bits
b1 b0
0
0 Single-chip mode
0
1
0
1
Not available
b7
b0
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.
Do not use these when an RC oscillation is selected.
Switch the clock division ratio
selection bits (bits 6 and 7 of CPUM)
Main routine
Switch to other mode except a ring oscillator
(Select one of 1/1, 1/2, and 1/8)
Note. After releasing reset the operation starts by starting a ring oscillator automatically.
Do not use a ring oscillator at ordinary operation.
After releasing reset
Start with a built-in ring oscillator ( Note)
Switch the oscillation mode
selection bit (bit 5 of CPUM)
Wait until establishment of
oscillator clock
An initial value is set as a ceramic oscillation
mode. When it is switched to an RC oscillation,
its oscillation starts.
Ceramic oscillation: wait time from oscillation start
until establishment of oscillation is required.
RC oscillation: wait time is not required basically
(oscillation is stabilized until the instruction to switch
is executed from a ring oscillator.)
FUNCTIONAL DESCRIPTION