Rainbow Electronics DS1780 - Manual (Page 8)

DS1780
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DS1780 MONITORING ORDER Table 3
TEMPERATURE READING
ANALOG +2.5 V
S
/V
CCP2
ANALOG +12V
ANALOG +5V
ANALOG +3.3V
ANALOG +2.5V
ANALOG +V
CCP1
FAN1
FAN2
If conversions are terminated by either of the methods described in the “OPERATION - Configuration
Register” section, the current “round-robin” loop will be completed and the results stored in RAM.
Monitoring will then terminate. When the monitoring again commences, monitoring always starts with
the temperature reading.
OPERATION - Temperature Data Format
The DS1780 internally converts measured temperature data to a two’s complement data format (in °C).
The host can read the last completed temperature conversion at any time by setting the Internal Address
Register pointer to location 27h, and reading the 8 bits in the register. The format of the data is shown
below in Table 4. The MSb of the register represents the sign bit of the temperature reading. For
Fahrenheit usage, a lookup table or conversion routine must be used.
TEMPERATURE/DATA RELATIONSHIPS Table 4
S 2 6 2 5 2 4 2 3 2 2 2 1 2 0
MSb (unit = °C) LSb
TEMPERATURE
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT (HEX)
+125°C 0111 1101 7Dh
+25°C 0001 1001 19h
+1°C 0000 0001 01h
0°C 0000 0000 00h
-1°C 1111 1111 FFh
-25°C 1110 0111 E7h
-40°C 1101 1000 D8h
OPERATION - Voltage Data Format
The DS1780 contains inputs for directly monitoring the power supplies typically found in a PC (+12V, -
12V, +5V, +3.3V, +2.5V, +V
CCP
). These inputs are scaled internally to a reference source, and converted
via an 8-bit Delta-Sigma ADC (Analog-to-Digital Converter), thus allowing for a more accurate means of
measurement since the voltages are referenced to a known value.
Since these inputs can be greater than V
DD
, they are not diode protected to the power rails. In addition,
small external series resistors such as 510Ω should be put into the lines driving the DS1780 to prevent
damaging the traces or power supplies should an accidental short connect two power supplies together.