23
3851 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
Fig. 23 Structure of I
2
C control register
[I
2
C Control Register (S1D)] 002E
16
The I
2
C control register (address 002E
16
) controls data communi-
cation format.
Bits 0 to 2: Bit counter (BC0–BC2)
These bits decide the number of bits for the next 1-byte data to be
transmitted. The I
2
C interrupt request signal occurs immediately
after the number of count specified with these bits (ACK clock is
added to the number of count when ACK clock is selected by ACK
clock bit (bit 7 of address 002F
16
)) have been transferred, and
BC0 to BC2 are returned to “000
2
”.
Also when a START condition is received, these bits become
“000
2
” and the address data is always transmitted and received in
8 bits.
Bit 3: I
2
C interface enable bit (ES0)
This bit enables to use the multi-master I
2
C-BUS interface. When
this bit is set to “0,” the use disable status is provided, so that the
SDA and the SCL become high-impedance. When the bit is set to
“1,” use of the interface is enabled.
When ES0 = “0,” the following is performed.
PIN = “1,” BB = “0” and AL = “0” are set (which are bits of the I
2
C
status register at address 002D
16
).
Writing data to the I
2
C data shift register (address 002B
16
) is dis-
abled.
Bit 4: Data format selection bit (ALS)
This bit decides whether or not to recognize slave addresses.
When this bit is set to “0,” the addressing format is selected, so
that address data is recognized. When a match is found between a
slave address and address data as a result of comparison or when
a general call (refer to “I
2
C Status Register,” bit 1) is received,
transfer processing can be performed. When this bit is set to “1,”
the free data format is selected, so that slave addresses are not
recognized.
Bit 5: Addressing format selection bit (10BIT SAD)
This bit selects a slave address specification format. When this bit
is set to “0,” the 7-bit addressing format is selected. In this case,
only the high-order 7 bits (slave address) of the I
2
C address regis-
ter (address 002C
16
) are compared with address data. When this
bit is set to “1,” the 10-bit addressing format is selected, and all
the bits of the I
2
C address register are compared with address
data.
Bit 6: SDA/SCL pin selection bit
This bit selects the input/output pins of SCL and SDA of the multi-
master I
2
C-BUS interface.
Bit 7: I
2
C-BUS interface pin input level selection bit
This bit selects the input level of the SCL and SDA pins of the
multi-master I
2
C-BUS interface.
Fig. 22 SDA/SCL pin selection bit
SCL
SDA
Multi-master
I C-BUS interface
TSEL
SCL
1
/P2
3
SCL
2
/TxD/P2
5
SDA
1
/P2
2
SDA
2
/RxD/P2
4
TSEL
TSEL
TSEL
b7
TISS TSEL
10 BIT
SAD
ALSES0 BC2 BC1 BC0
b0
SDA/SCL pin selection bit
0 : Connect to ports P2
2
, P2
3
1 : Connect to ports P2
4
, P2
5
I
2
C control register
(S1D : address 002E
16
)
Bit counter (Number of
transmit/receive bits)
b2 b1 b0
0
0
0 : 8
0
0
1 : 7
0
1
0 : 6
0
1
1 : 5
1
0
0 : 4
1
0
1 : 3
1
1
0 : 2
1
1
1 : 1
I
2
C-BUS interface
enable bit
0 : Disabled
1 : Enabled
Data format selection bit
0 : Addressing format
1 : Free data format
Addressing format
selection bit
0 : 7-bit addressing
format
1 : 10-bit addressing
format
I
2
C-BUS interface pin input
level selection bit
0 : CMOS input
1 : SMBUS input