Datasheet
Dual, Temperature-Controlled Resistors with Inter-
nally Calibrated Monitors and Password Protection
10 Maxim Integrated
DS1856
Monitored Signals
Each signal (V
CC
, MON1, MON2, MON3, and tempera-
ture) is available as a 16-bit value with 12-bit accuracy
(left-justified) over the serial bus. See Table 1 for signal
scales and Table 2 for signal format. The four LSBs
should be masked when calculating the value. The 3
LSBs are internally masked with 0s.
The signals are updated every frame rate (t
frame
) in a
round-robin fashion.
The comparison of all five signals with the high and low
user-defined values are done automatically. The corre-
sponding flags are set to 1 within a specified time of
the occurrence of an out-of-limit condition.
Calculating Signal Values
The LSB = 100µV for V
CC
, and the LSB = 38.147µV for
the MON signals when using factory default settings.
To calculate V
CC
, convert the unsigned 16-bit value to
decimal and multiply by 100µV.
To calculate MON1, MON2, or MON3, convert the
unsigned 16-bit value to decimal and multiply by
38.147µV.
To calculate the temperature, treat the two’s comple-
ment value binary number as an unsigned binary num-
ber, then convert to decimal and divide by 256. If the
result is greater than or equal to 128, subtract 256 from
the result.
Temperature: high byte: -128°C to +127°C signed; low
byte: 1/256°C.
SIGNAL
+FS
SIGNAL
+FS
(hex)
-FS
SIGNAL
-FS
(hex)
Temperature
+127.984°
7FFC
-128°C 8000
V
CC
6.5528V FFF8
0V 0000
MON1
2.4997V FFF8
0V 0000
MON2
2.4997V FFF8
0V 0000
MON3
2.4997V FFF8
0V 0000
Table 1. Scales for Monitor Channels at
Factory Setting
SIGNAL FORMAT
V
CC
Unsigned
MON1 Unsigned
MON2 Unsigned
MON3 Unsigned
Temperature Two’s complement
Table 2. Signal Comparison
TEMPERATURE
(°C)
CORRESPONDING LOOK-UP
TABLE ADDRESS
<-40 80h
-40 80h
-38 81h
-36 82h
-34 83h
——
+98 C5h
+100 C6h
+102 C7h
>+102 C7h
Table 3. Look-Up Table Address for
Corresponding Temperature Values
MSB
2
15
2
14
2
13
2
12
2
11
2
10
2
9
2
8
LSB
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSB (BIN) LSB (BIN) VOLTAGE (V)
10000000 10000000 3.29
11000000 11111000 4.94
S2
6
2
5
2
4
2
3
2
2
2
1
2
0
2
-1
2
-2
2
-3
2
-4
2
-5
2
-6
2
-7
2
-8
MSB (BIN) LSB (BIN)
TEMPERATURE (°C)
01000000 00000000 +64
01000000 00001111 +64.059
01011111 00000000 +95
11110110 00000000 -10
11011000 00000000 -40
MSB (BIN) LSB (BIN) VOLTAGE (V)
11000000 00000000 1.875
10000000 10000000 1.255
Monitor/V
CC
Bit Weights
Temperature Bit Weights
Monitor Conversion Example
V
CC
Conversion Examples
Temperature Conversion Examples