AN1043

DS01043A-page 8

© 2006 Microchip Technology Inc.

HARDWARE ADDRESS PINS

multiple devices with the same base slave address to

operate on the bus.

Slave devices with SPI interfaces typically use only a

chip select pin to select the device. This requirement

consumes one MCU pin for every SPI device on the

bus.

The “S” devices (MCP23S08 and MCP23S17) have

SPI interfaces. These devices use a chip select for

selecting the part, however, these parts also have hard-

ware address pins, thereby giving the advantage of

attaching multiple devices on the bus while only

consuming one MCU pin for chip select (see Figure 9).

FIGURE 9:

ADDRESS PINS ON SPI DEVICES

SUMMARY

The MCP23X08/17 family of GPIO Expanders have

some unique features, giving the system and module

engineer maximum flexibility when designing with the

MCP23X08/17.

CS

SCK

SDI

SDO

SPI

A2

A1

A0

Addr

Pins

GPIO

Port

GP15

.

.

.

.

.

.

.

GP0

0 1 0 0 1

0

0

0 A

S

0 0 0 0 1

1

0

0 A

MCP23X17

Opcode

Register Addr

A2 A1 A0

MCP23S17

A1

A0

MCP23S08

GP7

.

.

.

GP0

MCP23S08