M37754 Mitsubishi, M37754 Datasheet - Page 66

• Manufacturer Part Number: M37754
• Description: SINGLE-CHIP 16BIT CMOS MICROCOMPUTER
• Manufacturer: Mitsubishi

CLOCK GENERATING CIRCUIT
The clock generating circuit makes basic clocks, which activate the
central processing unit (CPU), bus interface unit (BIU) and internal
peripheral devices, of an oscillation circuit output. Figure 82 shows
the block diagram of the clock generating circuit.
The clock source
source
When bit 6 (clock source select bit) of processor mode register 1 is
“0”, the clock which is obtained by dividing an input clock to the X
pin by 2 becomes the clock source
which is an input clock to the X
as it is. When bit 2 (clock source for peripheral devices select bit) is
“0”, the clock source
standard clock for peripheral devices. When bit 2 is “1”, the clock
source
is.
The standard clock is more divided with the division circuit shown in
Figure 82 and the clocks having all kinds of frequencies are made.
Each internal peripheral device can select one of 4 clocks, Pf
Pf
Pf
by 2 when the clock source for peripheral devices select bit is “1”. It
means f(X
MHz, fix the bit to “0”.
Figure 80 shows a circuit example using a ceramic (or quartz crys-
tal) resonator. Use the manufactures’ recommended values for con-
stants such as capacitance which differs for each resonator.
Figure 81 shows a circuit example inputting clocks externally. When
inputting clocks externally, setting bit 1 (clock external input select
bit) of particular function select register 0 (in Figure 83) to “1” makes
operation of the clock oscillation circuit stop, that is, the X
stays at “H”, and the current consumption reduce.
66
CPU
64
2
means f(X
and Pf
to activate the CPU are made of an clock input to the X
BIU
1
IN
becomes the standard clock for peripheral devices as it
512
) divided by 4 when that bit is “0”. In the case of
to activate the bus interface unit and the clock source
, and use it.
IN
), which is an oscillation circuit’s frequency, divided
1
to activate internal peripheral devices, the clock
1
which is more divided by 2 becomes the
IN
pin becomes the clock source
1
. When bit 6 is “1”, the clock
M37754M8C-XXXGP, M37754M8C-XXXHP
OUT
1
2
IN
> 12.5
output
, Pf
pin.
16
IN
1
,
Fig. 80 Circuit example using a ceramic (or quartz crystal) resonator
Fig. 81 Circuit example inputting clocks externally
M37754S4CGP, M37754S4CHP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
External clock source
Vcc
Vss
X
X
IN
IN
MITSUBISHI MICROCOMPUTERS
C
IN
R
f
X
X
Open
OUT
OUT
R
C
d
OUT