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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
7540 Group
MITSUBISHI MICROCOMPUTERS
8
PRELIMINARY
Notice: This is not a final specification.
Some parametric limits are subject to change.
FUNCTIONAL DESCRIPTION
Central Processing Unit (CPU)
The 7540 Group uses the standard 740 family instruction set. Refer
to the table of 740 family addressing modes and machine-language
instructions or the 740 Family Software MANUAL for details on each
instruction set.
Machine-resident 740 family instructions are as follows:
1. The FST and SLW instructions cannot be used.
2. The MUL and DIV instructions can be used.
3. The WIT instruction can be used.
4. The STP instruction can be used.
(This instruction cannot be used while CPU operates by a ring oscil-
lator.)
[CPU mode register] CPUM
The CPU mode register contains the stack page selection bit.
This register is allocated at address 003B
16
.
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. 9 Switching method of CPU mode register
Fig. 8 Structure of CPU mode register
Oscillation mode selection bit (Note 1)
0 : Ceramic oscillation
CPU mode register
(CPUM: address 003B
16
)
Stack page selection bit
0 : 0 page
Clock division ratio selection bits
b7 b6
φ
) = f(X
IN
)/2 (High-speed mode)
0 1 : f(
φ
) = f(X
IN
)/8 (Middle-speed mode)
1 0 : applied from ring oscillator
φ
) = f(X
IN
) (Double-speed mode)(Note 2)
Ring oscillator oscillation control bit
X
IN
oscillation control bit
0 : Ceramic or RC oscillation enabled
Processor mode bits (Note 1)
0 0 Single-chip mode
0 1
1 0
Not available
b7 b0
2:
These bits are used only when a ceramic oscillation is selected.
Do not use these when an RC 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”.)
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 a built-in ring oscillator
An initial value is set as a ceramic
oscillation mode. When it is switched to an
RC oscillation, its oscillation starts.
Switch to other mode except a ring oscillator.
At the same time, select the double-speed,
high-speed, or middle-speed mode.
Wait by ring 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 a ring oscillator meets the requirement).