AN1043

DS01043A-page 2

© 2006 Microchip Technology Inc.

FIGURE 1:

I/O PORT BLOCK DIAGRAM

8/16 BIT MODE (MCP23X17 ONLY)

The MCP23X17 has the unique ability to appear to the

MCU as either two (2) 8-bit GPIO expanders, or as a

single 16-bit GPIO expander.

This is accomplished by splitting the 16 I/O ports into

two separate 8-bit I/O ports (Port A and Port B) via

IOCON.bank.

Each port has a group of dedicated registers. Table 1

shows how the register groups (Port A and Port B) are

mapped when in 8-bit or 16-bit mode.

8-Bit Mode:

When in 8-bit mode, the ports’ registers are separated:

• Port A register addresses range from 00h – 0Ah

• Port B register addresses range from 10h – 1Ah

16-bit Mode:

When in 16-bit mode, the ports’ registers are

interleaved to emulate 16-bit wide registers:

• Port A and Port B register addresses range from

00h – 15h. The registers are still addressed as

8-bit ports, meaning that the 16-bit mapping pair

is always an even number (e.g., IODIR starts at

00h, IPOL starts at 02h, etc.)

TABLE 1:

MEMORY MAP

Note:

Unlike all other registers which are not

shared between the two ports (Port A and

Port B), there is one register (IOCON).

which is shared between the ports and

affects both equally.

Q

Q

SET

CLR

D

Q

Q

SET

CLR

D

Q

Q

SET

CLR

D

Input

Buffer

OLAT or

GPIO

IODIR

Data Bus

Write

Write

Read

Port

I/O

Pad

MCP23X08/17

8-bit Mode

16-bit Mode

Register

Name

Address

(hex)

Register

Name

Address

(hex)

IODIRA

00

IODIRA

00

IPOLA

01

IODIRB

01

GPINTENA

02

IPOLA

02

DEFVALA

03

IPOLB

03

INTCONA

04

GPINTENA

04

IOCON

05

GPINTENB

05

GPPUA

06

DEFVALA

06

INTFA

07

DEFVALB

07

INTCAPA

08

INTCONA

08

GPIOA

09

INTCONB

09

OLATA

0A

IOCON

0A

IODIRB

10

IOCON

0B

IPOLB

11

GPPUA

0C

GPINTENB

12

GPPUB

0D

DEFVALB

13

INTFA

0E

INTCONB

14

INTFB

0F

IOCON

15

INTCAPA

10

GPPUA

16

INTCAPB

11

INTFB

17

GPIOA

12

INTCAPB

18

GPIOB

13

GPIOB

19

OLATA

14

OLATB

1A

OLATB

15