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MCP23009T

8-Bit I/O Expander with Open-Drain Outputs

Microchip Technology 

MCP23009/MCP23S09

1.2 Power-On Reset (POR)

The on-chip POR circuit holds the device in reset until

VDD has reached a high enough voltage to deactivate

the POR circuit (i.e., release the device from reset).

The maximum VDD rise time is specified in the

electrical specification section.

When the device exits the POR condition (releases

reset), the device operating parameters (i.e., voltage,

temperature, serial bus frequency, etc.) must be met to

ensure proper operation.

1.3 Serial Interface

This block handles the functionality of the I2C

(MCP23009) or SPI (MCP23S09) interface protocol.

The MCP23X09 contains eleven (11) individual

registers which can be addressed through the Serial

Interface block (Table 1-3).

TABLE 1-3:

Address

00h

01h

02h

03h

04h

05h

06h

07h

08h

09h

0Ah

REGISTER ADDRESSES

Access to

IODIR

IPOL

GPINTEN

DEFVAL

INTCON

IOCON

GPPU

INTF

INTCAP (read-only)

GPIO

OLAT

1.3.1

BYTE MODE AND SEQUENTIAL

MODE

The MCP23X09 has the ability to operate in Byte mode

or Sequential mode (IOCON.SEQOP). Byte mode and

Sequential mode are not to be confused with I2C byte

operations and sequential operations. The modes

explained here relate to the device’s internal address

pointer and whether or not it is incremented after each

byte is clocked on the serial interface.

• Byte mode disables automatic address pointer

incrementing. When operating in Byte mode, the

MCP23X09 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.

DS20002121C-page 6

• Sequential mode enables automatic address

pointer incrementing. When operating in

Sequential mode, the MCP23X09 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, which are

serial protocol sequences. For example, the device

may be configured for Byte mode and the master may

perform a continuous read. In this case, the

MCP23X09 would not increment the address pointer

and would repeatedly drive data from the same

location.

1.3.2

I2C INTERFACE

1.3.2.1 I2C Write Operation

The I2C write operation includes the control byte and

the register address sequence, as shown in the bottom

of Figure 1-1. This sequence is followed by eight bits of

data from the master and an Acknowledge (ACK) from

the MCP23009. The operation is ended with a Stop (P)

or Restart (SR) condition being generated by the

master.

Data is written to the MCP23009 after every byte

transfer. If a Stop or Restart condition is generated

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

MCP23009.

Both Byte mode and Sequential mode are supported

by the MCP23009. If Sequential mode is enabled

(default), the MCP23009 increments its address

counter after each ACK during the data transfer.

1.3.2.2 I2C Read Operation

I2C read operations include the control byte sequence,

as shown in the bottom of Figure 1-1. This sequence is

followed by another control byte (including the Start

condition and ACK) with the R/W bit equal to a logic

one (R/W = 1). The MCP23009 then transmits the data

contained in the addressed register. The sequence is

ended with the master generating a Stop or Restart

condition.

1.3.2.3 I2C Sequential Write/Read

For sequential operations (Write or Read), instead of

transmitting a Stop or Restart condition after the data

transfer, the master clocks the next byte pointed to by

the address pointer (see Section 1.3.1 “Byte Mode

and Sequential Mode” for details regarding sequential

operation control).

The sequence ends with the master sending a Stop or

Restart condition.

The MCP23009 address pointer will roll over to

address zero after reaching the last register address.

Refer to Figure 1-1.

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