Siemens SINUMERIK 840 Planning Manual page 126

9 Appendix
9.1 Reception using the 3964R procedure
Character frame
In order to recognize each character again at the receiving end and to check error-free
transmission, further bits are added to the characters sent, either as prefix or suffix. Each
character to be transmitted begins with a start element and ends with at least one stop
element. The 3964R procedure uses 8 data bits. The parity bit is used to protect the data
against transmission errors.
I
mA
40
20
S A I 0
0
Start element
SA = start bit
I* = information bit
PA = parity bit
SO= stop bit
The control characters for the 3964R procedure are in accordance with the DIN 66003
standard for the 7-bit code. At the end of each data block a block check character (BCC) is
sent to secure the data.
For the information characters a code is not specified (code transparency).
Data protection
A parity bit is appended to the character to be transmitted for protecting the data against
transmission errors. Additionally, with the 3964R procedure, the sum of bits of equal value of
all characters in a block is complemented by a further bit. The resulting block check character
BCC itself is secured using the character parity method and transmitted at the end of the
block. All characters of the block except the STX start control character are covered by that
procedure.
9–4
I 1 I 2 I 3 I 4 I 5
8 Information bits
(8 Data bits)
Character frame 10 or 11 bits
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I 6 I 7 P A S O
Parity element
Stop element
Start element
6FC5 197-0AB20-0BP0
SINUMERIK 840/880 (PJ)
08.89
t