Appendix - Thermo Scientific Premium PC 200 Manual

Appendix

NOTE All byte values are shown in hex, hex represents the binary values that must be sent to the chiller.
Do not use ASCII.
The framing of the communications packet in both directions is:
Lead char Addr-MSB Addr-LSB Command
CA or CC
Lead char
Addr-msb
Addr-lsb
Command
n d-bytes
d-byte 1
...
d-byte n
Checksum
The master requests information by sending one of the Read Functions as shown in Table 1. Since
no data is sent to the chiller during a read request, the master uses 00 for the number of data bytes
following the command byte.
The chiller will respond to a Read Function by echoing the lead character, address, and command byte,
followed by the requested data and checksum. When the chiller sends data, a qualifier byte is sent first,
followed by a two byte signed integer (16 bit, MSB sent first). The qualifier byte indicates the precision
and units of measure for the requested data as detailed in Table 2.
As an RS-232 example, the master requests to read internal temperature unit address 01 by sending:
If the temperature is -12°C, the unit would reply:
CA 00 01 20 03 01 FF F4 E7
2

0 1
0xCA (RS-232) 0xCC (RS-485)
Device address is 1 (RS-232)
Most significant byte of device address (RS-232: 0).
Least significant byte of device address is 1 (RS-232).
Command byte (see Table 1).
Number of data bytes to follow (00 to 03 hex).
1 data byte (the qualifier byte is considered a data byte).
st
...
n data byte.
th
Bitwise inversion of the 1 byte sum of bytes beginning with the most
significant address byte and ending with the byte preceding the checksum.
(To perform a bitwise inversion, "exclusive OR" the one byte sum with FF hex.)
command byte
CA 00 01 20 00 DE
0 bytes of data
command byte
3 bytes to follow
Checksum region
n d-bytes d-byte 1
The checksum is the bitwise
inversion of 21
(00+01+20+00)
byte values are in hex
The qualifier byte of 01 indicates a precision of 0
decimal point and units of °C. The temperature of
-12°C is -12 decimal = FFF4 hex.
... d-byte n Checksum
The checksum is the bitwise inversion of 18
(00+01+20+03+01+FF+F4) = 218
Take the LSB = 18
Bitwise inversion = E7
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