MC74 Datasheet, PDF (7/12 Pages) ON Semiconductor – Serial Digital Temperature Sensor

MC74
REGISTER SET and PROGRAMMER’S MODEL
MC74 Command Set
(SMBus READ_BYTE and WRITE_BYTE)
Command Byte Description
Command Code Function
RTR
00h Read Temperature (TEMP)
RWCR
01h Read/Write Configuration (CONFIG)
Configuration Register (CONFIG), 8–BITS,
READ/WRITE
Configuration Register (Config)
D[7]
D[6] D[5] D[4] D[3] D[2] D[1] D[0]
SHDN Data Rdy Reserved
Bit
POR Function
Type Operation
D[7]
0 STANDBY switch Read/ 1 = standby,
Write 0 = normal
D[6]
0 Data Ready*
Read 1 = ready,
Only 0 = not ready
D[5]—D[0] 0 Reserved — Al-
N/A N/A
ways returns zero
when read.
*DATA_RDY bit reset at power–up and SHDN enable (see below).
V _DD
DATA_RDY
SHDN
t _conv
t _conv
Figure 3. . DATA_RDY, SHDN Operation Logic
Diagram
Temperature Register (TEMP), 8–Bits,
READ–ONLY
The binary value (2’s complement format) in this register
represents temperature of the integrated sensor following a
conversion cycle. The registers are automatically updated in
an alternating manner.
Temperature Register (TEMP)
D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0]
MSB x
x
x
x
x
x LSB
In the temperature data registers, each unit value
represents one degree (Celsius). The value is in
2’s–complement binary format such that a reading of 0000
0000b corresponds to 0°C. Examples of this temperature to
binary value relationship are shown in the following table.
Temperature–to–Digital Value Conversion (TEMP)
ACTUAL
TEMPERATURE
REGISTERED
TEMPERATURE
BINARY HEX
+130.00°C
+127°C
0111 1111
+127.00°C
+127°C
0111 1111
+126.50°C
+127°C
0111 1111
+25.25°C
+25°C
0001 1001
+0.50°C
+1°C
0000 0001
+0.25°C
0°C
0000 0000
0.00°C
0°C
0000 0000
-0.25°C
0°C
0000 0000
-0.50°C
0°C
0000 0000
-0.75°C
-1°C
1111 1111
-1.00°C
-1°C
1111 1111
-25.00°C
-25°C
1110 0111
-25.25°C
-25°C
1110 0110
-54.75°C
-55°C
1100 1001
-55.00°C
-55°C
1100 1001
-65.00°C
-65°C
1011 1111
Register Set Summary
The MC74’s register set is summarized below. All
registers are 8–bits wide.
Name Description
POR State Read Write
TEMP Internal sensor
0000 0000b* √
temperature (2’s
complement)
CONFIG CONFIG register 0000 0000b
√
√
*NOTE: The TEMP register immediately will be updated by the
A/D converter after the DATA_RDY bit goes high.
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