M37544 RENESAS [Renesas Technology Corp], M37544 Datasheet - Page 65

• Manufacturer Part Number: M37544
• Description: SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
• Manufacturer: RENESAS [Renesas Technology Corp]

Notes on Clock Generating Circuit
1. Switch of ceramic/quartz-crystal oscillation and RC oscillation
After releasing reset, the oscillation mode selection bit (bit 5 of
CPU mode register (address 3B
oscillation selected). When the RC oscillation is used, after releas-
ing reset, set this bit to “1”.
2. Double-speed mode
The double-speed mode can be used only when a ceramic oscilla-
tion is selected. Do not use it when an RC oscillation is selected.
3. CPU mode register
Oscillation mode selection bit (bit 5), processor mode bits (bits 1
and 0) of CPU mode register (address 3B
cillation mode and to control operation modes of the
microcomputer. In order to prevent the dead-lock by erroneously
writing (ex. program run-away), these bits can be rewritten only
once after releasing reset. After rewriting, it is disabled to write any
data to the bit. (The emulator MCU “M37542RSS” is excluded.)
Also, when the read-modify-write instructions (SEB, CLB, etc.) are
executed to bits 2 to 4, 6 and 7, bits 5, 1 and 0 are locked.
4. Clock division ratio, X
control
The state transition shown in Fig. 81 can be performed by setting
the clock division ratio selection bits (bits 7 and 6), X
control bit (bit 4), on-chip oscillator oscillation control bit (bit 3) of
CPU mode register. Be careful of notes on use in Fig. 81.
5. On-chip oscillator operation
When the MCU operates by the on-chip oscillator for the main
clock, connect X
leave X
The clock frequency of the on-chip oscillator depends on the sup-
ply voltage and the operation temperature range.
Be careful that this margin of frequencies when designing applica-
tion products.
6. Ceramic resonator
When the ceramic resonator/quartz-crystal oscillation is used for
the main clock, connect the ceramic resonator and the external
circuit to pins X
resistor is built-in.
7. RC oscillation
When the RC oscillation is used for the main clock, connect the
X
capacitor C at the shortest distance.
The frequency is affected by a capacitor, a resistor and a micro-
computer.
So, set the constants within the range of the frequency limits.
8. External clock
When the external signal clock is used for the main clock, connect
the X
Select “0” (ceramic oscillation) to oscillation mode selection bit.
Rev.1.04
REJ03B0012-0104Z
7544 Group
IN
pin and X
IN
OUT
pin to the clock source and leave X
pin open.
2004.06.08
OUT
IN
IN
and X
pin to the external circuit of resistor R and the
pin to V
OUT
IN
CC
page 65 of 66
oscillation control, on-chip oscillator
at the shortest distance. A feedback
through a 1 k
16
)) is “0” (ceramic/quartz-crystal
16
OUT
) are used to select os-
to 10 k
pin open.
IN
resistor and
oscillation
Notes on Oscillation Control
1. Oscillation stop detection circuit
(1) When the stop mode is used, set the oscillation stop detection
(2) When the ceramic or RC oscillation is stopped (bit 4 of CPU
(3) The oscillation stop detection circuit is not included in the emu-
2. Stop mode
(1) When the stop mode is used, set the oscillation stop detection
(2) When the stop mode is used, set “0” (STP instruction enabled)
(3) The oscillation stabilizing time after release of STP instruction
(4) The STP instruction cannot be used when the on-chip oscilla-
(5) When the stop mode is used, set the on-chip oscillator oscilla-
(6) Do not execute the STP instruction during the A/D conversion.
function to “invalid”.
mode register (address 3B
tion function to “invalid”.
lator MCU “M37542RSS”.
function to “invalid”.
to the STP instruction disable bit of the watchdog timer control
register (bit 6 of watchdog timer control register (address
39
can be selected from “set automatically”/“not set automati-
cally” by the oscillation stabilizing time set bit after release of
the STP instruction (bit 0 of MISRG (address 38
is set to this bit, “01
prescaler 1 automatically at the execution of the STP instruc-
tion. When “1” is set to this bit, set the wait time to timer 1 and
prescaler 1 according to the oscillation stabilizing time of the
oscillation. Also, when timer 1 is used, set values again to
timer 1 and prescaler 1 after system is returned from the stop
mode.
tor is selected by the clock division ratio selection bits (bits 7
and 6 of CPU mode register (address 3B
tion control bit (bit 3 of CPU mode register (address 3B
“1” (on-chip oscillator oscillation stop).
16
)).
16
” is set to timer 1 and “FF
16
)), set the oscillation stop detec-
16
)).
16
)). When “0”
16
” is set to
16
)) to