MCP9808 datasheet(14/52 Pages) MICROCHIP

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MCP9808

DS25095A-page 14

4.1.4

ADDRESS BYTE

Following the Start condition, the host must transmit an

8-bit address byte to the MCP9808. The address for the

MCP9808 temperature sensor is ‘0011,A2,A1,A0’ in

binary, where the A2, A1 and A0 bits are set externally

by connecting the corresponding pins to VDD ‘1’ or GND

‘0’. The 7-bit address, transmitted in the serial bit stream,

must match the selected address for the MCP9808 to

respond with an ACK. Bit 8 in the address byte is a

read/write bit. Setting this bit to ‘1’ commands a read

operation, while ‘0’ commands a write operation (see

Figure 4-1).

FIGURE 4-1:

Device Addressing.

4.1.5

DATA VALID

After the Start condition, each bit of data in the

transmission needs to be settled for a time specified by

tSU-DATA before SCL toggles from low-to-high (see the

Sensor Serial Interface Timing Specifications section).

4.1.6

ACKNOWLEDGE (ACK/NAK)

Each

receiving

device,

when

addressed,

must

generate an ACK bit after the reception of each byte.

The master device must generate an extra clock pulse

for ACK to be recognized.

The Acknowledging device pulls down the SDA line for

tSU-DATA before the low-to-high transition of SCL from

the master. SDA also needs to remain pulled down for

tH-DATA after a high-to-low transition of SCL.

During read, the master must signal an End-of-Data

(EOD) to the slave, by not generating an ACK bit

(NAK), once the last bit has been clocked out of the

slave. In this case, the slave will leave the data line

released to enable the master to generate the Stop

condition.

4.1.7

TIME-OUT

If the SCL stays low or high for the time specified by

tOUT, the MCP9808 temperature sensor resets the

serial interface. This dictates the minimum clock speed

as outlined in the specification.

234

5678

SCL

SDA

1 A2 A1 A0

Start

Address Byte

Slave

Address

R/W

MCP9808 Response

Code

Address

See Table 3-2.

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