3874 Group User’s Manual
3-27
APPENDIX
3.3 Notes on use
3.3.8 Notes on data link layer communication control circuit
(1)
Start and mode switch of data link layer communication control circuit
q The data link layer communication control is stopped after reset. Write “00XXXXX12” to the
communicatiton mode register to start the data link layer communication control circuit or switch
the mode. Bits 4 and 5 are read exclusive bits.
(2)
P75/BUSOUT pin and P76/BUSIN pin
q The P75/BUSOUT pin and the P76/BUSIN pin function as normal ports after reset released. When
selecting as normal ports, these pins can be switched to either input or output by the direction
register.
3.3.9 Notes on A-D converter
(1)
Analog input pin
Make the signal source impedance for analog input low, or equip an analog input pin with an external
capacitor of 0.01
F to 1F. Further, be sure to verify the operation of application products on the
user side.
q Reason
An analog input pin includes the capacitor for analog voltage comparison. 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 precision to be worse.
(2)
A-D converter power source pin
Pins AVSS are A-D converter power source pins. Regardless of using the A-D conversion function
or not, connect them as following :
AVSS : Connect to the VSS line
q Reason
If the AVSS pin are opened, the microcomputer may have a failure because of noise or others.
(3)
Reference voltage input pin VREF
When using A-D converter or D-A converter, apply a voltage of 2 V to Vcc to the reference voltage
input pin VREF. Note that if the VREF value is lowered, the accuracy degrades.
(4)
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. Thus, make sure the following during an A-D conversion.
f(XIN) is 500 kHz or more
Do not execute the STP instruction and WIT instruction
(5)
A-D/D-A conversion register
The A-D/D-A conversion register functions as an A-D conversion register during a read and a D-A
conversion during a write. Accordingly, the D-A conversion register set value cannnot be read out.
(6)
Inputting falling signal to ADT pin during A-D conversion when using external trigger
When inputting the falling signal to the ADT pin during A-D conversion, A-D conversion which is in
progress is stopped, and A-D conversion is started again.