Mitsubishi microcomputers
M16C / 62A Group (80-pin)
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
UART2 Special Mode Register
115
UART2 Special Mode Register
The UART2 special mode register (address 037716) is used to control UART2 in various ways.
Figure 1.14.25 shows the UART2 special mode register.
In the first place, the control bits related to the I2C bus(simplified I2C bus) interface are explained.
Bit 0 of the UART special mode register (037716) is used as the I2C mode selection bit.
Setting “1” in the I2C mode select bit (bit 0) goes the circuit to achieve the I2C bus (simplified I2C bus)
interface effective.
Table 1.14.9 shows the relation between the I2C mode select bit and respective control workings.
Since this function uses clock-synchronous serial I/O mode, set this bit to “0” in UART mode.
Figure 1.14.25. UART2 special mode register
UART2 special mode register
Symbol Address When reset
U2SMR 0377
16
00
16
b7 b6 b5 b4 b3 b2 b1 b0
Bit name
Bit
symbol WR
Function
(During UART mode)
Function
(During clock synchronous
serial I/O mode)
ABSCS
ACSE
SSS
I2C mode select bit
Bus busy flag
0 : STOP condition detected
1 : START condition detected
SCLL sync output
enable bit
Bus collision detect
sampling
clock select bit
Arbitration lost detecting
flag control bit
0 : Normal mode
1 : IIC mode
0 : Update per bit
1 : Update per byte
IICM
ABC
BBS
LSYN
0 : Ordinary
1 : Falling edge of RxD2
0 : Disabled
1 : Enabled
Transmit start condition
select bit
Must always be “0”
0 : Rising edge of transfer
clock
1 : Under flow signal of timer A0
Auto clear function
select bit of transmit
enable bit
0 : No auto clear function
1 : Auto clear at occurrence of
bus collision
Must always be “0”
Must always be “0”
Must always be “0”
Must always be “0”
Must always be “0”
Must always be “0”
Note 1: Nothing but “0” may be written.
Note 2: When not in I2C mode, do not set this bit by writing a “1”. During normal mode, fix it to “0”. When this
bit = “0”, UART2 special mode register 3 (U2SMR3 at address 0375
16
) bits 7 to 5 (DL2 to DL0 = SDA
digital delay setup bits) are initialized to “000”, with the analog delay circuit selected. Also, when SDDS
= “0”, the U2SMR3 register cannot be read or written to.
Note 3: When analog delay is selected, only the analog delay value is effective; when digital delay is selected,
only the digital delay value is effective.
(Note1)
SDDS SDA digital delay select
bit (Note 2, Note 3) Must always be “0”
0 : Analog delay output
is selected
1 : Digital delay output
is selected
(must always be “0” when
not using I C mode)
2
UART2 special mode register 3 (I C bus exclusive use register)
Symbol Address When reset
U2SMR3 0375
16
Indeterminate
(However, when SDDS = “1”, the initial value is “00
16
”)
b7 b6 b5 b4 b3 b2 b1 b0
Bit name
Bit
symbol WR
Function
(I C bus exclusive use register)
DL2
SDA digital delay setup
bit
(Note 1, Note 2, Note 3,
Note 4)
DL0
DL1
0 0 0 : Analog delay is selected
0 0 1 : 2 cycle of 1/f(X
IN
)
0 1 0 : 3 cycle of 1/f(X
IN
)
0 1 1 : 4 cycle of 1/f(X
IN
)
1 0 0 : 5 cycle of 1/f(X
IN
)
1 0 1 : 6 cycle of 1/f(X
IN
)
1 1 0 : 7 cycle of 1/f(X
IN
)
1 1 1 : 8 cycle of 1/f(X
IN
)
2
Nothing is assigned.
In an attempt to write to these bits, write “0”. The value, if read, turns out to be
indeterminate. However, when SDDS = “1”, the value “0” is read out (Note 1)
2
b7 b6 b5
Note 1: This bit can be read or written to when UART2 special mode register (U2SMR at address 0377
16
) bit
7 (SDDS: SDA digital delay select bit) = “1”. When the initial value of UART2 special mode register 3
(U2SMR3) is read after setting SDDS = “1”, the value is “00
16
”. When writing to UART2 special mode
register 3 (U2SMR3) after setting SDDS = “1”, be sure to write 0's to bits 0–4. When SDDS = “0”,
this register cannot be written to; when read, the value is indeterminate.
Note 2: These bits are initialized to “000” when SDDS = “0”, with the analog delay circuit selected. After a reset,
these bits are set to “000”, with the analog delay circuit selected. However, because these bits can be
read only when SDDS = “1”, the value read from these bits when SDDS = “0” is indeterminate.
Note 3: When analog delay is selected, only the analog delay value is effective; when digital delay is selected,
only the digital delay value is effective.
Note 4: The amount of delay varies with the load on SCL and SDA pins. Also, when using an external clock, the
amount of delay increases by about 100 ns, so be sure to take this into account when using the device.
Digital delay is
selected