LTC2983
19
2983fc
For more information www.linear.com/LTC2983
APPLICATIONS INFORMATION
Bits B4 to B0 determine which input channel the conversion
is performed upon and are simply the binary equivalent
of the channel number (see Table 7).
Bit B5 should be set to 0.
Bits B7 and B6 serve as start/done bits. In order to start
a conversion, these bits must be set to “10” (B7=1 and
B6=0). When the conversion begins, the INTERRUPT
pin goes LOW. Once the conversion is complete, bits B7
and B6 will toggle to “01” (B7=0 and B6=1) (Address =
0x000) and the INTERRUPT pin will go HIGH, indicating
the conversion is complete and the result is available.
State 4: Conversion
The measurement cycle starts after the initiate conversion
command is written into RAM location 0x000 (Table 6).
The LTC2983 simultaneously measures the selected input
sensor, sense resistors (RTDs and thermistors), and cold
junction temperatures if applicable (thermocouples).
Once the conversion is started, the user is locked out of
the RAM, with the exception of reading status data stored
in RAM memory location 0x000.
Once the conversion is started the INTERRUPT pin goes
low. Depending on the sensor configuration, two or three
82ms cycles are required per temperature result. These
correspond to conversion rates of 167ms and 251ms,
respectively. Details describing these modes are described
in the 2- and 3-cycle Conversion Modes section of the
data sheet.
The end of conversion can be monitored either through
the interrupt pin (LOW to HIGH transition), or by reading
the command status register in RAM memory location
0x000 (start bit, B7, toggles from 1 to 0 and DONE bit,
B6, toggles from 0 to 1).
State 5: Read Results
Once the conversion is complete, the conversion results
can be read from RAM memory locations corresponding
to the input channel (see Table 8).
The conversion result is 32 bits long and contains both
the sensor temperature (D23 to D0) and sensor fault data
(D31 to D24) (see Tables 9A and 9B).
Table 8. Conversion Result Memory Map
CONVERSION
CHANNEL
START
ADDRESS
END ADDRESS SIZE (BYTES)
CH1 0x010 0x013 4
CH2 0x014 0x017 4
CH3 0x018 0x01B 4
CH4 0x01C 0x01F 4
CH5 0x020 0x023 4
CH6 0x024 0x027 4
CH7 0x028 0x02B 4
CH8 0x02C 0x02F 4
CH9 0x030 0x033 4
CH10 0x034 0x037 4
CH11 0x038 0x03B 4
CH12 0x03C 0x03F 4
CH13 0x040 0x043 4
CH14 0x044 0x047 4
CH15 0x048 0x04B 4
CH16 0x04C 0x04F 4
CH17 0x050 0x053 4
CH18 0x054 0x057 4
CH19 0x058 0x05B 4
CH20 0x05C 0x05F 4
The result is reported in °C for all temperature sensors with a
range of –273.16°C to 8192°C and 1/1024°C resolution or in
°F with a range of –459.67°F to 8192°F with 1/1024°F reso-
lution. Included with the conversion result are seven sensor
fault bits and a valid bit. These bits are set to a 1 if there was a
problem associated with the corresponding conversion result
(see Table 10). Two types of errors are reported: hard errors
and soft errors. Hard errors indicate the reading is invalid
and the resulting temperature reported is –999°C or °F. Soft
errors indicate operation beyond the normal temperature
range of the sensor or the input range of the ADC. In this
case, the calculated temperature is reported but the ac-
curacy may be compromised. Details relating to each fault
type are sensor specific and are described in detail in the
sensor specific sections of this data sheet. Bit D24 is the
valid bit and will be set to a 1 for valid data.
Once the data read is complete, the device is ready for a new
initiate conversion command. In cases where new channel
configuration data is required, the user has access to the
RAM in order to modify existing channel assignment data.
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