MCP4441 datasheet(54/100 Pages) MICROCHIP

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MCP444X/446X

DS22265A-page 54

6.2

I2C Operation

The MCP44XX’s I2C module is compatible with the

Philips I2C specification. The following lists some of the

modules features:

• 7-bit slave addressing

• Supports three clock rate modes:

- Standard mode, clock rates up to 100 kHz

- Fast mode, clock rates up to 400 kHz

- High-speed mode (HS mode), clock rates up

to 3.4 MHz

• Support Multi-Master Applications

• General call addressing

• Internal weak pull-ups on interface signals

The I2C 10-bit addressing mode is not supported.

The Philips I2C specification only defines the field

types, field lengths, timings, etc. of a frame. The frame

content defines the behavior of the device. The frame

content for the MCP44XX is defined in Section 7.0.

6.2.1

I2C BIT STATES AND SEQUENCE

Figure 6-8 shows the I2C transfer sequence. The serial

clock is generated by the master. The following defini-

tions are used for the bit states:

• Start bit (S)

• Data bit

• Acknowledge (A) bit (driven low) /

No Acknowledge (A) bit (not driven low)

• Repeated Start bit (Sr)

• Stop bit (P)

6.2.1.1

Start Bit

The Start bit (see Figure 6-2) indicates the beginning of

a data transfer sequence. The Start bit is defined as the

SDA signal falling when the SCL signal is “High”.

FIGURE 6-2:

Start Bit.

6.2.1.2

Data Bit

The SDA signal may change state while the SCL signal

is Low. While the SCL signal is High, the SDA signal

MUST be stable (see Figure 6-5).

FIGURE 6-3:

Data Bit.

6.2.1.3

Acknowledge (A) Bit

The A bit (see Figure 6-4) is typically a response from

the receiving device to the transmitting device.

Depending on the context of the transfer sequence, the

A bit may indicate different things. Typically the Slave

device will supply an A response after the Start bit and

8 “data” bits have been received. an A bit has the SDA

signal low.

FIGURE 6-4:

Acknowledge Waveform.

Not A (A) Response

The A bit has the SDA signal high. Table 6-1 shows

some of the conditions where the Slave Device will

issue a Not A (A).

If an error condition occurs (such as an A instead of A),

then an START bit must be issued to reset the

command state machine.

TABLE 6-1:

MCP45XX/MCP46XX A / A

RESPONSES

SDA

SCL

1st Bit

2nd Bit

SDA

SCL

Data Bit

1st Bit

2nd Bit

Event

Acknowledge

Bit

Response

Comment

General Call

Only if GCEN bit is

set

Slave Address

valid

Slave Address

not valid

Device Mem-

ory Address

and specified

command

(AD3:AD0 and

C1:C0) are an

invalid combi-

nation

After device has

received address

and command

Communica-

tion during

EEPROM write

cycle

After device has

received address

and command,

and valid condi-

tions for EEPROM

write

Bus Collision

N.A.

I2C Module

Resets, or a “Don’t

Care” if the colli-

sion occurs on the

Master’s “Start bit”

SDA

SCL

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