Experimental Physics and
Industrial Control System

Gerrit Kühn <[email protected]> · Wed, 1 Aug 2012 14:43:34 +0200

On Tue, 31 Jul 2012 16:30:05 +0200 Dirk Zimoch <[email protected]> wrote
about Re: stream device string/hex parsing:

DZ> > The documentation says the packet LRC is the two's complement of the
DZ> > sum over the packet's parameter and command bytes. Each binary data
DZ> > byte is transmitted as two hex digits which have to be transformed
DZ> > into binary form before adding them. So, looking at the available
DZ> > checksum algorithms, this calls for something like %<neghexsum8>,
DZ> > which does not exist...

DZ> %0<negsum>

Hm... not quite:

2012/08/01 14:33:43.162 ADC16_W Input byte 0xE7 does not match checksum
0xFC
2012/08/01 14:33:43.162 ADC16_S Input byte 0xEC does not match
checksum 0x01
2012/08/01 14:33:41.162 ADC16_C Input byte 0xD7 does not match checksum
0xFB

The description for <negsum> is

---
One byte. The negative of the sum of all characters modulo 2^8
---

However, I do not need to sum over all characters, I need to interpret
every two characters as hex value, sum over these, invert and compare the
result with the hex value represented by the two checksum characters. Or
am I misunderstanding something here?

cu
  Gerrit

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System