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3. APPENDIX
MITSUBISHI MICROCOMPUTER
3819 Group
3.1 Notes on use
3819 Group USER’S MANUAL
<Note 2>
When the data register (port latch) of an I/O port is modified with the bit managing instruction*, the value of the
unspecified bit may be changed.
Reason
The bit managing instructions are read-modify-write form instructions for reading and writing data by a byte unit.
Accordingly, when these instructions are executed on a bit of the data register of an I/O port, the following is executed
to all bits of the data register.
qAs for a bit which is set to an input port : The pin state is read in the CPU, and is written to this bit after bit managing.
qAs for a bit which is set to an output port : The bit value is read in the CPU, and is written to this bit after bit managing.
Note the following :
qEven when a port which is set as an output port is changed for an input port, its data register holds the output data.
qAs for a bit of which is set to an input port , its value may be changed even when not specified with a bit managing
instruction in case where the pin state differs from its data register contents
* bit managing instructions : SEB and CLB instruction
<Note 3>
When not using the A-D converter, connect the A-D converter power source AVSS pin as follows :
qAVSS : Connect to the VSS pin
Reason
If the AVSS pin is opened, the microcomputer may have a failure because of noise or others.
3.1.6 Notes on clock synchronous serial I/O
<Note>
When an external clock is used as the synchronous clock for data transmission, set the transmit enable bit to “1” at
“H” of the SCLK input level. Also, write data to the transmit buffer register at “H” of the SCLK input level.