Datasheet

MCP9808
DS25095A-page 14 © 2011 Microchip Technology Inc.
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 V
DD
‘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
t
SU-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
t
SU-DATA
before the low-to-high transition of SCL from
the master. SDA also needs to remain pulled down for
t
H-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
t
OUT
, the MCP9808 temperature sensor resets the
serial interface. This dictates the minimum clock speed
as outlined in the specification.
123456789
SCL
SDA
011A2A1A0
Start
Address Byte
Slave
Address
R/W
MCP9808 Response
Code
Address
A
C
K
0
See Table 3-2.