MCP23018T-ESLASHSP datasheet(7/56 Pages) MICROCHIP

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DS22103A-page 7

MCP23018/MCP23S18

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), 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

(MCP23018) or SPI (MCP23S18) interface protocol.

The MCP23X18 contains twenty two (22) individual

registers (eleven [11] register pairs) which can be

addressed through the Serial Interface block (Table 1-

1).

TABLE 1-1:

1.3.1

BYTE MODE AND SEQUENTIAL

MODE

The MCP23X18 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 incre-

menting.

When

operating

Byte

Mode,

the

MCP23X18 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 associ-

ated 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, the address

pointer can initially point to either address in the regis-

ter pair.

Sequential Mode enables automatic address pointer

incrementing. When operating in Sequential Mode, the

MCP23X18 increments its address counter after each

byte during the data transfer. The address pointer auto-

matically 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

continuous

read.

this

case,

the

MCP23X18 would not increment the address pointer

and would repeatedly drive data from the same loca-

tion.

1.3.2

I2C INTERFACE

1.3.2.1

I2C Write Operation

The I2C write operation includes the control byte and

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

data from the master and an Acknowledge (ACK) from

the MCP23018. The operation is ended with a stop (P)

or restart (SR) condition being generated by the mas-

ter.

Data is written to the MCP23018 after every byte trans-

fer. If a stop or restart condition is generated during a

data transfer, the data will not be written to the

MCP23018.

Both “byte mode” and “sequential mode” are supported

by the MCP23018. If sequential mode is enabled

(default), the MCP23018 increments its address

counter after each ACK during the data transfer.

Address

IOCON.BANK = 1

Address

IOCON.BANK = 0

Access to:

00h

IODIRA

10h

01h

IODIRB

01h

02h

IPOLA

11h

03h

IPOLB

02h

04h

GPINTENA

12h

05h

GPINTENB

03h

06h

DEFVALA

13h

07h

DEFVALB

04h

08h

INTCONA

14h

09h

INTCONB

05h

0Ah

IOCON

15h

0Bh

IOCON

06h

0Ch

GPPUA

16h

0Dh

GPPUB

07h

0Eh

INTFA

17h

0Fh

INTFB

08h

10h

INTCAPA

18h

11h

INTCAPB

09h

12h

GPIOA

19h

13h

GPIOB

0Ah

14h

OLATA

1Ah

15h

OLATB

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