
Serial Communication
149
Specifications in this manual are tentative and subject to change
Rev. E
MITSUBISHI MICROCOMPUTERS
M30245 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
UARTi Special Mode Register 2
Bit 0 is the I2C mode select bit 2. Table 1.50 lists the control changes by bit when the I2C mode select bit is
“1”. Start and stop condition detection timing characteristics are shown in Figure 1.108.
Table 1.50. Functions changed by I2C mode select bit 2
Function
IICM2=0
IICM2=1
Interrupt numbers 13, 15, 17, 19
factor
Acknowledge not detected (NACK)
UARTi transfer (rising edge of the
last bit)
Interrupt number 2, 8, 10, 21 factor
Acknowledge detected (ACK)
UARTi receive (falling edge of the
last bit)
DMA factor
Acknowledge detected (ACK)
UARTi receive (falling edge of the
last bit)
Data transfer timing from UART
receive shift register to receive buffer
Rising edge of the last bit of receive
clock
Rising edge of the last bit of receive
clock
UART receive/ACK interrupt request
generation timing
Rising edge of the last bit of receive
clock
Rising edge of the last bit of receive
clock
Set up time
Hold time
SCL
SDA
(Start condition)
SDA
(Stop condition)
3 to 6 cyles < set up time (Note)
3 to 6 cycles < hold time (Note)
Note: Cycle number shows main clock input oscillation frequency f(Xin) cycle number.
Figure 1.108. Start/stop condition detect timing characteristics
Bit 1 is the clock synchronizing bit. When this bit is set to “1”, if the falling edge is detected at pin SCLi
while the internal SCL is “H”, the internal SCL is changed to “L”, the baud rate generator value is reloaded
and the L sector count starts. Also, while the SCLi pin is “L”, if the internal SCL changes from “L” to “H”,
baud rate generator stops counting. If the SCLi pin is “H”, counting restarts. Because of this function, the
UARTi transmit/receive clock takes the AND condition for the internal SCL and SCLi pin signals. This
function operates from the clock half period before the first rise of the UARTi clock to the 9th rise. To use
this function, select the internal clock as the transfer clock.
Bit 2 is the SCL wait output bit. When this bit is set to “1”, output from the SCLi pin is fixed to “L” at the
clock’s 9th fall. When set to “0”, the “L” output lock is released.
Bit 3 is the SDA output stop bit. When this bit is set to “1”, an arbitration lost generated. If the arbitration lost
detection flag is “1”, the SDAi pin simultaneously becomes high impedance.
Bit 4 is the UARTi initialize bit. While this bit is set to “1”, the following operations are performed when the
start condition is detected.
The transmit shift register is initialized and the content of the transmission register is transmitted to the
transmission shift register. Transmission starts with the first bit of the next input clock. However, the UARTi
output value does not change when the start condition is detected. It also doesn’t change when the clock is
input and when the first bit of data is output.