41
3886 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
[I
2
C Data Shift Register (S0)] 0012
16
The I
2
C data shift register (S0 : address 0012
16
) is an 8-bit shift
register to store receive data and write transmit data.
When transmit data is written into this register, it is transferred to
the outside from bit 7 in synchronization with the S
CL
clock, and
each time one-bit data is output, the data of this register are
shifted by one bit to the left. When data is received, it is input to
this register from bit 0 in synchronization with the S
CL
clock, and
each time one-bit data is input, the data of this register are shifted
by one bit to the left. The minimum 2 cycles of
φ
are required from
the rising of the S
CL
clock until input to this register.
The I
2
C data shift register is in a write enable status only when the
I
2
C-BUS interface enable bit (ES0 bit : bit 3 of address 15
16
) of
the I
2
C control register is “1.” The bit counter is reset by a write in-
struction to the I
2
C data shift register. When both the ES0 bit and
the MST bit of the I
2
C status register (address 0014
16
) are “1,” the
S
CL
is output by a write instruction to the I
2
C data shift register.
Reading data from the I
2
C data shift register is always enabled re-
gardless of the ES0 bit value.
[I
2
C Address Register (S0D)] 0013
16
The I
2
C address register (address 0013
16
) consists of a 7-bit slave
address and a read/write bit. In the addressing mode, the slave ad-
dress written in this register is compared with the address data to be
received immediately after the START condition is detected.
Bit 0: Read/write bit (RBW)
This is not used in the 7-bit addressing mode. In the 10-bit ad-
dressing mode, the first address data to be received is compared
with the contents (SAD6 to SAD0 + RBW) of the I
2
C address reg-
ister.
The RBW bit is cleared to “0” automatically when the stop condi-
tion is detected.
Bits 1 to 7: Slave address (SAD0–SAD6)
These bits store slave addresses. Regardless of the 7-bit address-
ing mode and the 10-bit addressing mode, the address data
transmitted from the master is compared with the contents of
these bits.
Fig. 36 Structure of I
2
C address register
S
A
D
6 S
A
D
5 S
A
D
4 S
A
D
3 S
A
D
2 S
A
D
1 S
A
D
0 R
B
W
S
l
a
v
e
a
d
d
r
e
s
s
I
2
C
(
S
a
D
d
:
d
a
r
d
e
d
s
s
e
r
s
e
s
g
0
i
s
0
t
1
e
r
0
r
3
1
6
)
R
e
a
d
/
w
r
i
t
e
b
i
t
b
7
b0