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flow_control: CRC documentation from modbus specifications

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This commit is contained in:
Markus Rosenstihl 2016-02-18 20:39:28 +00:00
parent 5f8f390434
commit e34103c367
1 changed files with 40 additions and 38 deletions
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12
src/tools/flow_control.py
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@ -10,7 +10,14 @@ import time
DEBUG = False DEBUG = False
crc_test = "\x0d\x01\x00\x62\x00\x33"
crc_expected = 0xddd
def crc(message):
""" """
(from "Modbus_over_serial_line_V1_02.pdf" at http://www.modbus.org)
6.2.2 CRC Generation 6.2.2 CRC Generation
==================== ====================
The Cyclical Redundancy Checking (CRC) field is two bytes, containing a 16–bit binary value. The CRC value is calculated by the The Cyclical Redundancy Checking (CRC) field is two bytes, containing a 16–bit binary value. The CRC value is calculated by the
@ -48,11 +55,6 @@ When the 16–bit CRC (two 8–bit bytes) is transmitted in the message, the low
order byte. order byte.
""" """
crc_test = "\x0d\x01\x00\x62\x00\x33"
crc_expected = 0xddd
def crc(message):
crc = 0xffff # step 1 crc = 0xffff # step 1
for byte in message: for byte in message:
if type(byte) == type(str): if type(byte) == type(str):