MCP23008/MCP23S08
DS21919E-page 8
2007 Microchip Technology Inc.
1.4.1
ADDRESSING I2C DEVICES
(MCP23008)
The MCP23008 is a slave I2C device that supports 7-bit
slave addressing, with the read/write bit filling out the
control byte. The slave address contains four fixed bits
and three user-defined hardware address bits (pins A2,
A1 and A0).
Figure 1-2 shows the control byte format.
1.4.2
ADDRESSING SPI DEVICES
(MCP23S08)
The MCP23S08 is a slave SPI device. The slave
address contains five fixed bits and two user-defined
hardware address bits (pins A1 and A0), with the read/
write bit filling out the control byte.
Figure 1-3 shows
the control byte format.
FIGURE 1-2:
I2C CONTROL BYTE
FORMAT
FIGURE 1-3:
SPI CONTROL BYTE
FORMAT
FIGURE 1-4:
I2C ADDRESSING REGISTERS
FIGURE 1-5:
SPI ADDRESSING REGISTERS
S
0
1
0
A2A1A0 R/W ACK
Start
bit
Slave Address
R/W bit
ACK bit
Control Byte
R/W = 0 = write
R/W = 1 = read
0
1000
A1 A0 R/W
Slave Address
R/W bit
Control Byte
R/W = 0 = write
R/W = 1 = read
CS
S0
1
0
A2 A1 A0
0
ACK
A7A6A5A4
A3A2A1A0
ACK
Device Opcode
Register Address
R/W = 0
The ACKs are provided by the MCP23008.
0100
0
A1 A0 R/W
A7
A6
A5
A4
A3
A2
A1
A0
Device Opcode
Register Address
CS