Rainbow Electronics DS1857 - Manual (Page 9)

DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
_____________________________________________________________________ 9
Monitored Signals
Each signal (V CC , MON1, MON2, and temperature) is
available as a 16-bit value with 12-bit accuracy (left-jus-
tified) 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 signals are updated every frame rate (t frame ) in a
round-robin fashion.
The comparison of all four 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.
To calculate the value of V CC , convert the unsigned 16-
bit value to decimal and multiply by 100µV.
To calculate the value of MON1 or MON2, convert the
unsigned 16-bit value to decimal and multiply by
38.147µV.
To calculate the value of the temperature, treat the
two’s complement value binary number as an unsigned
binary number, then convert to decimal and divide by
256. If the result is greater than or equal to 128, then
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 127.996 °C 7FFF -128 °C 8000
V CC 6.55V FFFF 0V 0000
MON1 2.5V FFFF 0V 0000
MON2 2.5V FFFF 0V 0000
Table 1. Scales for Monitor Channels
SIGNAL FORMAT
V CC Unsigned
MON1 Unsigned
MON2 Unsigned
Temperature Two’s complement
Table 2. Signal Comparison
TEMPERATURE
CORRESPONDING LOOK-UP
TABLE ADDRESS
<-40 °C 80h
-40 °C 80h
-38 °C 81h
-36 °C 82h
-34 °C 83h
— —
+98 °C C5h
+100 °C C6h
+102 °C C7h
>+102 °C 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
S 2 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
Temperature Conversion Example
V
CC
Conversion Example
Monitor Conversion Example