3-30
Driving the Display
PX 30 and PX 120 Operating Manual
Example for calculating the check sum CRC
Example 1 (BCD-coded text call-up) on page 3-26 shows how the check sum CRC is
calculated.
First of all, calculate the sum total (Σ) of all bytes from byte 2 (slave address / ID-Byte) up
to and including the last data byte (Data (DL); Byte 7 in the example).
To calculate the check sum CRC, follow the procedure depicted below, using the sum
total (Σ).
In Example 1: Byte 2 08
H
Byte 3 03
H
Byte 4 00
H
Byte 5 50
H
Byte 6 08
H
Byte 7 01
H
Σ =64
H
= 100
D
CRC = (255 - 100 + 1)
D
= 156
D
CRC = (FF - 64 + 01)
H
= 9C
H
Text Display Address and ID-Signal
The text display address and ID-Signal are transmitted in Byte 2 of the send telegram
(slave address/ID-Byte). Coding is as follows:
Text display address ID-Signal
7 6 5 4 3 2 1 0 Slave address Bit / ID-Byte
Address 1 0 0 0 0 1 0 0 0 ID-Signal 0
Address 2 0 0 0 1 0 0 0 1 ID-Signal 1
. . . . . . . . .
Address 31 1 1 1 1 1 1 1 1 ID-Signal 7 = Global Call
START
Σ > 255
?
Σ = Σ - 256
Σ > 0
?
CRC = 0 CRC = 255 - Σ + 1
END
yes
yes
no
no
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