Datasheet

MCP23008/MCP23S08
DS21919E-page 8 © 2007 Microchip Technology Inc.
1.4.1 ADDRESSING I
2
C DEVICES
(MCP23008)
The MCP23008 is a slave I
2
C 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: I
2
C™ CONTROL BYTE
FORMAT
FIGURE 1-3: SPI CONTROL BYTE
FORMAT
FIGURE 1-4: I
2
C™ ADDRESSING REGISTERS
FIGURE 1-5: SPI ADDRESSING REGISTERS
S 0 1 0 0 A2A1A0R/WACK
Start
bit
Slave Address
R/W bit
ACK bit
Control Byte
R/W = 0 = write
R/W = 1 = read
01000A1A0R/W
Slave Address
R/W bit
Control Byte
R/W = 0 = write
R/W = 1 = read
CS
S0100A2A1A00ACKA7A6A5A4A3A2A1A0ACK
Device Opcode
Register Address
R/W = 0
The ACKs are provided by the MCP23008.
01000A1A0R/W A7A6A5A4A3A2A1A0
Device Opcode Register Address
CS