UART2 Special Mode Register
140
Mitsubishi microcomputers
M16C / 62N Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
UART2 Special Mode Register
The UART2 special mode register (address 037716) is used to control UART2 in various ways.
Figure 1.17.26 shows the UART2 special mode register.
Bit 0 of the UART2 special mode register (037716) is used as the I2C mode select 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 1.17.9 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 1.17.26. UART2 special mode register
UART2 special mode register
Symbol
Address
When reset
U2SMR
037716
8016
b7
b6
b5
b4 b3
b2
b1
b0
Bit
name
Bit
symbol
W
R
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
SCL L sync output
enable bit
Bus collision detect
sampling clock select bit
Arbitration lost detecting
flag control bit
0 : Normal mode
1 : I2C 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 : Underflow 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”
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 037516) bits 7 to 5 (DL2 to DL0 = SDA
digital delay setup bits) are initialized to “000”. Also, when SDDS = “0”, the U2SMR3 register cannot be
read or written to.
(Note1)
SDDS
SDA digital delay select
bit (Note 2)
Must always be “0”
0 : Must always be “0”
when not using I2C mode
1 : Digital delay output
is selected
UART2 special mode register 3 (I C bus exclusive use register)
Symbol
Address
When reset
U2SMR3
037516
0016
b7
b6 b5
b4
b3
b2
b1
b0
Bit name
Bit
symbol
W
R
Function
(I C bus exclusive use register)
DL2
SDA digital delay setup
bit
(Note 1, Note 2, Note 3)
DL0
DL1
0 0 0 : Must not be set when using I2C mode
0 0 1 : 1 to 2 cycle(s) of 1/f(XIN)
0 1 0 : 2 to 3 cycles of 1/f(XIN)
0 1 1 : 3 to 4 cycles of 1/f(XIN)
1 0 0 : 4 to 5 cycles of 1/f(XIN)
1 0 1 : 5 to 6 cycles of 1/f(XIN)
1 1 0 : 6 to 7 cycles of 1/f(XIN)
1 1 1 : 7 to 8 cycles of 1/f(XIN)
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 037716) 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 “0016”. 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”. After a reset, these bits are set to “000”. However,
because these bits can be read only when SDDS = “1”, the value read from these bits when SDDS = “0”
is indeterminate.
Note 3: 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 200 ns, so be sure to take this into account when using the device.
Digital delay
is selected