
Serial I/O Mode 2
Specifications in this manual are tentative and subject to change
Rev. E
MITSUBISHI MICROCOMPUTERS
M30245 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
214
Standard serial I/O mode 2
In standard serial I/O mode 2 (clock asynchronous), software commands, addresses and data are
input and output between the MCU and peripheral units (serial programmer, etc.) using 2-wire
clock-asynchronous serial I/O (UART1).
Standard serial I/O mode is entered by releasing the reset with the P65 (CLK1) pin at a “L” level.
The TxD1 pin is set to CMOS output. Data transfer is in 8-bit units with LSB first, 1 stop bit and
parity OFF.
After reset, connections can be established at 9,600 bps when initial communications are made
with a peripheral unit. This requires a main clock with a minimum 2 MHz input oscillation fre-
quency. The baud rate can also be changed from 9,600 bps to 19,200, 38,400, or 57,600 bps by
executing software commands. Communication errors may occur because of the main clock
oscillation frequency. If errors occur, change the main clock’s oscillation frequency and the baud
rate.
After executing commands from a peripheral unit that require time to erase and write data, as
with the erase and program commands, allow a sufficient time interval or execute the read status
command and check how the processing ended before executing the next command.
Data and status registers can be read after transmitting software commands. Reading the status
register can check status of the flash memory operating state or successful completion of a
program or erase operation.
Initial communications with peripheral units
After reset, the bit rate generator is adjusted to 9,600 bps to match the main clock’s oscillation
frequency, by sending the code as prescribed by the protocol for initial communications with
peripheral units. Figure 1.169 shows the initial communication with peripheral units.
(1) Transmit “0016” from a peripheral unit 16 times. (The MCU with internal flash memory sets the
bit rate generator so that “0016” can be successfully received.)
(2) The MCU with internal flash memory outputs the “B016” check code and initial communica-
tions end successfully. Initial communications must be transmitted at a speed of 9,600 bps and a
transfer interval of a minimum 15 ms. Also, the baud rate at the end of initial communications is
9,600 bps.
Note. If the peripheral unit cannot receive “B016” successfully, change the oscillation frequency of
the main clock.
Figure 1.169. Peripheral unit and initial communication
MCU with internal
flash memory
Peripheral unit
(1) Transfer "00 16" 16 times
At least 15ms
transfer interval
1st
2nd
15 th
16th
(2) Transfer check code "B0 16"
"0016"
"B016"
"0016"
Reset
The bit rate generator setting completes (9600bps)