Thermo Scientific ULT-80 Installation & Operation Manual page 56

NOTE: All byte values are shown in hex, hex represents the binary values that must be sent to the bath. Do
not use ASCII.
The framing of the communications packet in both directions is:
Lead char Addr-MSB
CA 00
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 bath during a read request, the master uses 00 for the number of data bytes following the com-
mand byte.
The bath will respond to a Read Function by echoing the lead character, address, and command byte, followed
by the requested data and checksum. When the bath 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 -10.5°C, the bath would reply:
CA 00 01 20 03 11 FF 97 34
NC Serial Communications Protocol
Checksum region
Addr-LSB Command
01
CA (hex).
Device address is 1
Most significant byte of device address is 00 hex.
Least significant byte of device address is 01 hex.
Command byte (see Table 1).
Number of data bytes to follow (00 to 03 hex).
1 st data byte (the qualifier byte is considered a data byte).
...
n th data byte.
Bitwise inversion of the 1 byte sum of bytes beginning with the most signifi-
cant 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
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 11 indicates a precision of 1
decimal point and units of °C. The temperature of
-10.5°C is -105 decimal = FF97 hex.
The checksum is the bitwise inversion of
CB (00+01+20+03+11+FF+97)
- 28 -
... d-byte n Checksum