LM77

www.ti.com

SNIS103F – JUNE 1999 – REVISED MARCH 2013

Reading the LM77 can take place either of two ways: If the location latched in the Pointer is correct (most of the

time it is expected that the Pointer will point to the Temperature register because it will be the data most

frequently read from the LM77), then the read can simply consist of an address byte, followed by retrieving the

corresponding number of data bytes. If the Pointer needs to be set, then an address byte, pointer byte, repeat

start, and another address byte plus required number of data bytes will accomplish a read.

The first data byte is the most significant byte with most significant bit first, permitting only as much data as

necessary to be read to determine the temperature condition. For instance, if the first four bits of the temperature

data indicates a critical condition, the host processor could immediately take action to remedy the excessive

temperature. At the end of a read, the LM77 can accept either Acknowledge or No Acknowledge from the Master

(No Acknowledge is typically used as a signal for the slave that the Master has read its last byte).

An inadvertent 8-bit read from a 16-bit register, with the D7 bit low, can cause the LM77 to stop in a state where

the SDA line is held low as shown in Figure 9. This can prevent any further bus communication until at least 9

additional clock cycles have occurred. Alternatively, the master can issue clock cycles until SDA goes high, at

which time issuing a “Stop” condition will reset the LM77.

Figure 9. Inadvertent 8-Bit Read from 16-Bit Register where D7 is Zero (“0”)

(Selects which registers will be read from or written to):

Table 1. POINTER REGISTER

P7

P6

P5

P4

P3

P2

P1

P0

0

0

0

0

0

Register Select

P0–P2: Register Select:

P2

P1

P0

Register

0

0

0

Temperature (Read only) (Power-up default)

0

0

1

Configuration (Read/Write)

0

1

0

0

1

1

T_CRIT (Read/Write)

1

0

0

1

0

1

P3–P7: Must be kept zero.

Table 2. TEMPERATURE REGISTER (Read Only):

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Sign

Sign

Sign

Sign

MSB

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

CRIT

HIGH

LOW

Status Bits

D0–D2: Status Bits

D3–D15: Temperature Data. One LSB = 0.5°C. Two's complement format.

Table 3. CONFIGURATION REGISTER (Read/Write):

D7

D6

D5

D4

D3

D2

D1

D0

0

0

0

Fault Queue

INT Polarity

T_CRIT_A

INT Mode

Shutdown

Polarity

Copyright © 1999–2013, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: LM77