MAX7321AEE+ Datasheet MAX7321ATE+T, MAX7321AEE+, MAX7321ATE+ | P10-P12

MAX7321

Accessing the MAX7321

The MAX7321 is accessed through an I

C interface. The

transition flags are cleared, and INT is deasserted each

time the device acknowledges the I

C slave address.

A single-byte read from the MAX7321 returns the sta-

tus of the eight I/O ports.

A 2-byte read returns first the status of the eight I/O

ports (as for a single-byte read), followed by the transi-

tion flags.

A multibyte read (more than 2 bytes before the I

STOP bit) repeatedly returns the port data, alternating

with the transition flags. As the port data is resampled

for each transmission, and the transition flags are reset

each time, a multibyte read continuously returns the

current data and identifies any changing ports.

If a port data change occurs during the read sequence,

INT is reasserted after the I

C STOP bit. The MAX7321

does not generate another interrupt during a single-

byte or multibyte read.

Port data is sampled during the preceding I

acknowledge bit (the acknowledge bit for the I

C slave

address in the case of a single-byte or 2-byte read).

A single-byte write to the MAX7321 sets the logic state

of all eight I/O ports.

A multibyte write to the MAX7321 repeatedly sets the

logic state of all eight I/O ports.

Reading from the MAX7321

A read from the MAX7321 starts with the master trans-

mitting the MAX7321’s slave address with the R/W bit

set high. The MAX7321 acknowledges the slave

address, and samples the ports during the acknowl-

edge bit. INT deasserts during the slave address

acknowledge.

Typically, the master reads 1 or 2 bytes from the

MAX7321, each byte being acknowledged by the mas-

ter upon reception with the exception of the last byte.

When the master reads 1 byte from the MAX7321 and

subsequently issues a STOP condition (Figure 6), the

MAX7321 transmits the current port data, clears the

change flags, and resets the transition detection. INT

deasserts during the slave acknowledge. The new

snapshot data is the current port data transmitted to the

master; therefore, port changes ocurring during the

transmission are detected. INT remains high until the

STOP condition.

The master can read 2 bytes from the MAX7321 and

then issue a STOP condition (Figure 7). In this case, the

MAX7321 transmits the current port data, followed by the

change flags. The change flags are then cleared, and

transition detection resets. INT goes high (high imped-

ance if an external pullup resistor is not fitted) during the

slave acknowledge. The new snapshot data is the cur-

rent port data transmitted to the master; therefore, port

changes occurring during the transmission are detected.

INT remains high until the STOP condition.

C Port Expander with 8 Open-Drain I/Os

10 ______________________________________________________________________________________

SDA

SCL

DATA LINE STABLE;

DATA VALID

CHANGE OF DATA

ALLOWED

Figure 3. Bit Transfer

SCL

SDA BY

TRANSMITTER

CLOCK PULSE

FOR ACKNOWLEDGMENT

START

CONDITION

SDA BY

RECEIVER

12 89

Figure 4. Acknowledge

MAX7321

C Port Expander with 8 Open-Drain I/Os

______________________________________________________________________________________ 11

SDA

SCL

A2 A1 A0

R/W

MSB

LSB

ACK

Figure 5. Slave Address

SCL

MAX7321 SLAVE ADDRESS

S1 1 0 A

PORT I/O

P2P3P4P5

D0D1D2D3D4D5D6D7

PORT I/O

INT OUTPUT

R/W

PORT SNAPSHOT

PSU

INT REMAINS HIGH UNTIL STOP CONDITION

DATA

Figure 6. Reading the MAX7321 (1 Data Byte)

SCL

MAX7321 SLAVE ADDRESSS110

PORTS

INT OUTPUT

R/W

PORT SNAPSHOT

AD0D1D2D3D4D5D6D7

PORT SNAPSHOT

PSU

D7 D6 D5 D4 D3 D2 D1 D0 N

PORT SNAPSHOT

INT REMAINS HIGH UNTIL STOP CONDITION

S = START CONDITION

P = STOP CONDITION

SHADED = SLAVE TRANSMISSION

N = NOT ACKNOWLEDGE

I2I3I4I5

F2F3F4F5

PORT I/O INTERRUPT FLAGS

Figure 7. Reading the MAX7321 (2 Data Bytes)

MAX7321

Writing to the MAX7321

A write to the MAX7321 starts with the master transmit-

ting the MAX7321’s slave address with the R/W bit set

low. The MAX7321 acknowledges the slave address,

and samples the ports (takes a snapshot) during

acknowledge. INT goes high (high impedance if an

external pullup resistor is not fitted) during the slave

acknowledge. Typically, the master proceeds to trans-

mit 1 or more bytes of data. The MAX7321 acknowl-

edges these subsequent bytes of data and updates the

I/O ports with each new byte until the master issues a

STOP condition (Figure 8).

Applications Information

Port Input and I

C Interface Level

Translation from Higher or Lower

Logic Voltages

The MAX7321’s SDA, SCL, AD0, AD2, RST, INT, and I/O

ports P0–P7 are overvoltage protected to +6V indepen-

dent of V+. This allows the MAX7321 to operate from a

lower supply voltage, such as +3.3V, while the I

C inter-

face and/or any of the eight I/O ports are driven as inputs

driven from a higher logic level, such as +5V.

The MAX7321 can operate from a higher supply volt-

age, such as +3V, while the I

C interface and/or some

of the I/O ports P0–P7 are driven from a lower logic

level, such as +2.5V. Apply a minimum voltage of 0.7 x

V+ to assert a logic-high on any I/O port. For example,

a MAX7321 operating from a +5V supply may not rec-

ognize a +3.3V nominal logic-high. One solution for

input-level translation is to drive MAX7321 I/Os from

open-drain outputs. Use a pullup resistor to V+ or a

higher supply to ensure a high logic voltage greater

than 0.7 x V+.

Port-Output Port-Level Translation

The open-drain output architecture allows for level

translation to higher or lower voltages than the

MAX7321’s supply. Use an external pullup resistor on

any output to convert the high-impedance logic-high

condition to a positive voltage level. The resistor can be

connected to any voltage up to +6V, and the resistor

value chosen to ensure no more than 20mA is sunk in

the logic-low condition. For interfacing CMOS inputs, a

pullup resistor value of 220kΩ is a good starting point.

Use a lower resistance to improve noise immunity, in

applications where power consumption is less critical,

or where a faster rise time is needed for a given capac-

itive load.

Each of the I/O ports P0–P7 has a protection diode to

GND (Figure 9). When a port is driven to a voltage

lower than GND, the protection diode clamps the volt-

age to a diode drop below GND.

Each of the I/O ports P0–P7 also has a 40kΩ (typ) pullup

resistor that can be enabled or disabled. When a port is

driven to a voltage higher than V+

the body diode of the

pullup enable switch conducts and the 40kΩ pullup

resistor is enabled. When the MAX7321 is powered

down (V+ = 0), each I/O port appears as a 40kΩ resistor

in series with a diode connected to zero. I/O ports are

protected to +6V under any of these circumstances

(Figure 9).

C Port Expander with 8 Open-Drain I/Os

12 ______________________________________________________________________________________

SCL

SDA

START CONDITION R/W

SLAVE ADDRESS

12345678

AAA

DATA 1 DATA 2

DATA TO PORT DATA TO PORT

DATA 2 VALIDDATA 1 VALID

INTERNAL WRITE

TO PORT

DATA OUT

FROM PORT

S = START CONDITION SHADED = SLAVE TRANSMISSION

P = STOP CONDITION N = NOT ACKNOWLEDGE

Figure 8. Writing to the MAX7321

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

MAX7321AEE+

Mfr. #:

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Maxim Integrated

Description:

Interface - I/O Expanders I2C Port Expander w/8 Open-Drain I/Os

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MAX7321AEE+

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