M38203M4 Datasheet, PDF (225/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.5 Serial I/O1
2.5.5 Notes on use
(1) Notes on clock selection
The 3820 group can select either internal clock or external clock as a synchronizing clock. When an
external clock is selected as an synchronizing clock in the clock synchronous mode, note the follow-
ing.
sIn the clock synchronous mode
ŒFor an external clock source, when the duty cycle is 50%, use the following clock.
1.25 MHz or less....... at VCC = 4.0 V to 5.5 V
500 kHz or less.........at VCC = 2.5 V to 4.0 V
To change the duty cycle, set the both “H” and “L” widths as follows.
370 ns min. ............. at VCC = 4.0 V to 5.5 V
950 ns min. ............. at VCC = 2.5 V to 4.0 V
The shift operation of the transmit shift register or the receive shift register is continued while
synchronizing clocks are input to the serial I/O1 circuit. Accordingly, stop a synchronizing clock input
after 8 clocks are input.
When the internal clock is selected, the synchronizing clock input is automatically stopped.
ŽTo select an external clock as a synchronizing clock at data transmission, set the transmit enable
bit to “1” and write data into the transmit buffer register while the SCLK1 signal is “H.”
When an external clock is selected as a synchronizing clock in the UART mode, note the following.
sIn the UART mode
For an external clock source, when the duty ratio is 50%, use the following clock.
5 MHz or less.....at VCC = 4.0 V to 5.5 V
2 MHz or less.....at VCC = 2.5 V to 4.0 V
To change the duty cycle, set the “H” and “L” widths as follows.
93 ns min. ........at VCC = 4.0 V to 5.5 V
238 ns min. ........at VCC = 2.5 V to 4.0 V
(2) For serial I/O1 transmit or receive interrupts
ŒFor a serial I/O1 transmit interrupt, set a value in the serial I/O1 control register, then set the serial
I/O1 transmit interrupt request bit (bit 3 at address 003C16) to “0” with the CLB instruction.
After setting Œ, set the serial I/O1 transmit enable bit (bit 3 at address 003E16) to “1.”
ŽFor a serial I/O1 receive interrupt, set a value in the serial I/O1 control register, then set the serial
I/O1 receive interrupt request bit (bit 2 at address 003C16) to “0” with the CLB instruction.
After setting Ž, set the serial I/O1 receive interrupt enable bit (bit 2 at address 003E16) to “1.”
(3) Transmit interrupt request when the transmit enable bit is “1”
When the transmit enable bit is set to “1,” the transmit buffer empty flag and the transmit shift register
shift completion flag are set to “1.” Accordingly, even if either timing is selected as transmit interrupt
generating timing, an serial I/O1 transmit interrupt request occurs and the serial I/O1 transmit interrupt
request bit is set to “1.”
To use a serial I/O1 transmit interrupt, set the transmit enable bit to “1,” then set the serial I/O1
transmit interrupt request bit to “0” once. After that, set the serial I/O1 transmit interrupt enable bit to
“1” (interrupts enabled).
3820 GROUP USER’S MANUAL
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