Datasheet

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 T
HYST
(Read/Write)
0 1 1 T_CRIT (Read/Write)
1 0 0 T
LOW
(Read/Write)
1 0 1 T
HIGH
(Read/Write)
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
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