© 2006 Microchip Technology Inc.

DS01043A-page 5

AN1043

INTERNAL ADDRESS POINTER

CONTROL

Some slave serial devices automatically increment

their internal address pointer after each byte is clocked

by the master. This allows the master to sequentially

access multiple registers without re-sending the write

or read command.

Other slave devices do not automatically increment

their internal address pointer.

The MCP23X08/17 family of devices have the ability to

do either by configuring a control bit (IOCON.SEQOP).

This allows maximum flexibility when accessing the

registers.

For example, when configuring the device, it may be

desirable to allow the address pointer to automatically

increment so the device does not have to be re-

addressed after every byte.

Likewise, when performing a continuous operation on

a register (e.g., changing the outputs on a regular basis

by writing to GPIO or OLAT), it may be beneficial to

disable the address incrementing feature so that the

register is always accessed without re-addressing the

register.

FIGURE 5:

8-BIT MODE: ADDRESS POINTER DISABLED (MCP23008 EXAMPLE)

0 1 0 0 a

a

a

0 A

S

0 0 0 0 1

1

0

0 A 1 0 1 0 1

1

0

0 A 0 1 0 1 0

0

1

1 A 1 0 1 0 1

1

0

0 P

MCP23X08

Opcode

Register

Addr = 09h

Data @

09h

Data @

09h

Data @

09h

8-bit mode, the address pointer will not increment the

address pointer.

GPIOA

09

OLATA

0A

IODIRB

10

IPOLB

11

GPINTENB

12

DEFVALB

13

INTCONB

14

IOCON

15

GPPUB

16

INTFB

17

INTCAPB

18

GPIOB

19

OLATB

1A

See Figure 5 and Figure 6 for address pointer examples for the

MCP23X08 8-bit devices and Figure 7 and Figure 8 for the

MCP23X17 examples.