M38002M4 Datasheet, PDF (121/173 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
3.3 Notes on use
(3) Stop of data transmission and reception in a clock synchronous serial I/O mode
As for the serial I/O that can be used as either a clock synchronous or an asynchronous (UART) serial I/O, clear
both the transmit enable bit and receive enable bit to “0” (transmit and receive disabled) at the same time in the
following case:
q when stopping data transmission and reception during transmitting and receiving data in the clock synchronous
mode (when data is transmitted and received in the clock synchronous serial I/O mode, any one of data
transmission and reception cannot be stopped.)
Reason
In the clock synchronous serial I/O mode, the same clock is used for transmission and reception. If any one of
transmission and reception is disabled, a bit error occurs because transmission and reception cannot be
synchronized.
In this mode, the clock circuit of the transmission circuit also operates for data reception. Accordingly, the
transmission circuit does not stop by clearing only the transmit enable bit to “0” (transmit disabled). Also, the
transmission circuit is not initialized by clearing the serial I/O enable bit to “0” (serial I/O disabled) (refer to (1)).
(4) The SRDY pin on a receiving side
When signals are output from the SRDY pin on the reception side by using an external clock in the clock
synchronous serial I/O mode, set all of the receive enable bit, the SRDY output enable bit, and the transmit enable
bit to “1” (transmit enabled).
(5) Stop of data reception in a clock synchronous
serial I/O mode
Set the serial I/O control register again after the
transmission and the reception circuits are reset by
clearing both the transmit enable bit and the receive
enable bit to “0.”
Clear both the transmit
enable bit (TE) and the
receive enable bit (RE) to “0”
Set the bits 0 to 3 and bit 6 of
the serial I/O control register
Set both the transmit enable
bit (TE) and the receive
enable bit (RE) to “1”
Can be set with the
LDM instruction at
the same time
(6) Control of data transmission using the transmit shift completion flag
The transmit shift completion flag changes from “1” to “0” with a delay of 0.5 to 1.5 shift clocks. When checking
the transmit shift completion flag after writing a data to the transmit buffer register for controlling a data
transmission, note this delay.
(7) Control of data transmission using an external clock
When an external clock is used as the synchronous clock for data transmission, set the transmit enable bit to “1”
at “H” level of the SCLK input signal. Also, write data to the transmit buffer register at “H” level of the SCLK input
signal.
3.3.3 Notes on the RESET pin
When a rising time of the reset signal is long, connect a ceramic 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, make
sure the following :
qMake the length of the wiring which is connected to a capacitor the shortest possible.
qMake sure to check the operation of application products on the user side.
Reason
If the several nanosecond or several ten nanosecond impulse noise enters the RESET pin, a microcomputer may
malfunction.
3800 GROUP USER’S MANUAL
3-19