MCP23017-ESLASHML datasheet(13/42 Pages) MICROCHIP

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DS20001952C-page 13

MCP23017/MCP23S17

3.2.1

BYTE MODE AND SEQUENTIAL

MODE

The MCP23X17 family has the ability to operate in Byte

mode or Sequential mode (IOCON.SEQOP).

Byte mode disables automatic Address Pointer

incrementing. When operating in Byte mode, the

MCP23X17 family does not increment its internal

address counter after each byte during the data

transfer. This gives the ability to continually access the

same address by providing extra clocks (without

additional control bytes). This is useful for polling the

GPIO register for data changes or for continually

writing to the output latches.

A special mode (Byte mode with IOCON.BANK = 0)

causes the address pointer to toggle between

associated A/B register pairs. For example, if the BANK

bit is cleared and the Address Pointer is initially set to

address 12h (GPIOA) or 13h (GPIOB), the pointer will

toggle between GPIOA and GPIOB. Note that the

Address Pointer can initially point to either address in

the register pair.

Sequential mode enables automatic address pointer

incrementing. When operating in Sequential mode, the

MCP23X17 family increments its address counter after

each byte during the data transfer. The Address Pointer

automatically rolls over to address 00h after accessing

the last register.

These two modes are not to be confused with single

writes/reads and continuous writes/reads that are

serial protocol sequences. For example, the device

may be configured for Byte mode and the master may

perform

continuous

read.

this

case,

the

MCP23X17 would not increment the Address Pointer

and would repeatedly drive data from the same

location.

3.2.2

I2C INTERFACE

3.2.2.1

I2C Write Operation

The I2C write operation includes the control byte and

This sequence is followed by eight bits of data from the

master

and

Acknowledge

(ACK)

from

the

MCP23017. The operation is ended with a Stop (P) or

Restart (SR) condition being generated by the master.

Data is written to the MCP23017 after every byte

transfer. If a Stop or Restart condition is generated

during a data transfer, the data will not be written to the

MCP23017.

Both

“byte

writes”

and

“sequential

writes”

are

supported by the MCP23017. If Sequential mode is

enabled

(IOCON,

SEQOP = 0) (default),

the

MCP23017 increments its address counter after each

ACK during the data transfer.

FIGURE 3-1:

BYTE AND SEQUENTIAL WRITE

ADDR

DIN

....

ADDR

DIN

Byte

Sequential

ADDR

DIN

- Start

- Restart

- Stop

- Write

- Read

- Device opcode

- Device register address

- Data out from MCP23017

- Data in to MCP23017

DOUT

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