Float transmission order can be changed as described in Float transmission (Page 83).
Following example describes the Big-Endian representing of float IEEE741.
Value (decimal)
IEEE FP B MSB LSB
Register N
Register N + 1
high
low
high
low
100.0
42C80000h
42h
C8h
00h
00h
55.32
425D47AEh
42h
5Dh
47h
AEh
2.0
40000000h
40h
00h
00h
00h
1.0
3F800000h
3Fh
80h
00h
00h
-1.0
BF800000h
bFh
80h
00h
00h
Read absolute massflow (4.03001)
Query:
01,03,0B,B8,00,02,46,0A
Response:
01,03,04,40,C3,52,93,62,C8
Absolute mass‐
flow =
6.10383 kg/s
B.5
CRC calculation
The Cyclical Redundancy Checking (CRC) field is two bytes, containing a 16–bit binary value. The
CRC value is first generated by the transmitting device, which appends the CRC to the message.
The receiving device recalculates a CRC during receipt of the message, and compares the
calculated value to the actual value it received in the CRC field. If the two values are not equal an
error occurs.
In the following a short text description of how the CRC is calculated is provided. This description
is then followed by a C programming example.
CRC calculation
1. Load a 16–bit register with FFFF hex (all 1’s). Call this the CRC register.
2. Exclusive OR the first 8–bit byte of the message with the low–order byte of the 16–bit CRC
register, putting the result in the CRC register.
3. Shift the CRC register one bit to the right (toward the LSB), zero–filling the MSB. Extract and
examine the LSB.
4. (If the LSB was 0): Repeat Step 3 (another shift). (If the LSB was 1): Exclusive OR the CRC
register with the polynomial value 0xA001 (1010 0000 0000 0001).
5. Repeat Steps 3 and 4 until 8 shifts have been performed. When this is done, a complete 8–bit
byte will have been processed.
6. Repeat Steps 2 through 5 for the next 8–bit byte of the message. Continue doing this until all
bytes have been processed.
7. The final content of the CRC register is the CRC value.
8. When the CRC is placed into the message, its upper and lower bytes must be swapped as
described below.
Technical reference
B.5 CRC calculation
SITRANS MASS 2100 & FC300 (FCT010/DSL)
Operating Instructions, 06/2020, A5E39788682-AB
147