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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 n d-bytes d-byte 1 ... d-byte n Checksum
CA
0
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 example, the master requests to read internal temperature by sending:
CA 00 01 20 00 DE
If the temperature is -12°C, the chiller would reply:
CA 00 01 20 03 01 FF F4 E7
A - 2
Merlin
Checksum region
1
CA (hex).
Device address is 1
Most significant byte of device address is 0.
Least significant byte of device address is 1.
Command byte (see Table 1).
Number of data bytes to follow (00 to 03 hex).
st
1
data byte (the qualifier byte is considered a data byte).
...
th
n
data byte.
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
0 bytes of data
command
byte
3 bytes to follow
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.
The checksum is the bitwise inversion of
18 (00+01+20+03+01+FF+F4) = 218
Take the LSB = 18
Bitwise inversion = E7
Thermo Scientific
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