M37544 RENESAS [Renesas Technology Corp], M37544 Datasheet - Page 64

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

Rev.1.04
REJ03B0012-0104Z
7544 Group
4. I/O pin function when serial I/O is enabled.
The pin functions of P1
follows according to the setting values of a serial I/O mode selec-
tion bit (bit 6 of serial I/O control register (address 1A
serial I/O synchronous clock selection bit (bit 1 of serial I/O control
register).
(1) Serial I/O mode selection bit
Clock synchronous type serial I/O is selected.
• Setup of a serial I/O synchronous clock selection bit
“0” : P1
“1” : P1
• Setup of a S
“0” : P1
“1” : P1
(2) Serial I/O mode selection bit
Clock asynchronous (UART) type serial I/O is selected.
• Setup of a serial I/O synchronous clock selection bit
“0”: P1
“1”: P1
• When clock asynchronous (UART) type serial I/O is selected, it
Notes on A/D conversion
1. Analog input pin
In order to execute the A/D conversion correctly, to complete the
charge to an internal capacitor within the specified time is re-
quired. The maximum output impedance of the analog input
source required to complete the charge to a capacitor within the
specified time is as follows;
About 35 k
When the maximum output impedance exceeds the above value,
equip an analog input pin with an external capacitor of 0.01 F to
1 F between an analog input pin and V
Further, be sure to verify the operation of application products on
the user side.
<Reason>
An analog input pin includes the capacitor for analog voltage com-
parison. Accordingly, when signals from signal source with high
impedance are input to an analog input pin, charge and discharge
noise generates. This may cause the A/D conversion/comparison
precision to be worse.
2. Clock frequency during A/D conversion
The comparator consists of a capacity coupling, and a charge of
the capacity will be lost if the clock frequency is too low. This may
cause the A/D conversion precision to be worse. Accordingly, set
f(X
during A/D conversion.
functions P1
IN
) in order that the A/D conversion clock is 500 kHz or over
2
2
2
2
3
3
pin can be used as a normal I/O pin.
pin turns into an input pin of an external clock.
pin turns into an output pin of a synchronous clock.
pin turns into a S
pin turns into an input pin of a synchronous clock.
pin can be used as a normal I/O pin.
2004.06.08
(at f(X
RDY
3
pin. It can be used as a normal I/O pin.
output enable bit (SRDY)
IN
) = 8 MHz)
2
/S
RDY
CLK
page 64 of 66
output pin.
and P1
“1” :
“0” :
3
SS
/S
.
RDY
are switched to as
16
)) and a
3. A/D conversion accuracy
As for AD translation accuracy, on the following operating condi-
tions, accuracy may become low.
(1) Since the analog circuit inside a microcomputer becomes sen-
(2) When V
Notes on Watchdog Timer
1. The watchdog timer is operating during the wait mode. Write
2. The watchdog timer stops during the stop mode. However, the
3. The STP instruction disable bit (bit 6 of watchdog timer control
Notes on RESET pin
1. Connecting capacitor
In case where the RESET signal rise time is long, connect a ce-
ramic capacitor or others across the RESET pin and the Vss pin.
And use a 1000 pF or more capacitor for high frequency use.
When connecting the capacitor, note the following :
• Make the length of the wiring which is connected to a capacitor
• Be sure to verify the operation of application products on the
<Reason>
If the several nanosecond or several ten nanosecond impulse
noise enters the RESET pin, it may cause a microcomputer fail-
ure.
as short as possible.
user side.
data to the watchdog timer control register to prevent timer un-
derflow.
watchdog timer is running during the oscillation stabilizing time
after the STP instruction is released. In order to avoid the un-
derflow of the watchdog timer, the watchdog timer control
register must be written just before executing the STP instruc-
tion.
register (address 39
“0” by program.
sitive to noise when V
voltage, accuracy may become low rather than the case
where V
value.
low temperature may become extremely low compared with
that at room temperature. When the system would be used at
low temperature, the use at V
mended.
REF
REF
voltage is lower than [ 3.0 V ], the accuracy at the
voltage and Vcc voltage are set up to the same
16
)) can be set to “1” but cannot be set to
REF
voltage is set up lower than Vcc
REF
=3.0 V or more is recom-