Rainbow Electronics DS1859 - Manual (Page 10)

DS1859
Dual, Temperature-Controlled Resistors with
Internally Calibrated Monitors
10 ____________________________________________________________________
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.
For the 20k
Ω version, 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 °C 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
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
Monitor Conversion Example
V CC Conversion Examples
Temperature Conversion Examples