EUCHNER CIS3(A) - Manual (Page 7)

EUCHNER Identsystem CIS3
071652-01-8/99 Subject to technical modifications page 7 / 23
4.2 Special features of the 3964-R data transfer protocol /1/
The 3964-R data transfer protocol is a comparatively reliable program for electronic data
interchange between a control and a connected peripheral since data transfer is handled with
a standardised protocol.
On controls with integrated 3964-R driver (see /1/ for instance), it is not necessary for the
user to bother with the details of connection set-up and cleardown resp. data integrity.
It suffices to transfer the telegram core to the 3964-R driver via the program.
On controls without 3964-R driver or if a read/write head is connected to PC’s, the user must,
however, also program the connection set-up and cleardown and the retry attempts.
4.2.1 Basic information on data transfer procedures with protocol /1/
Numerous conventions must be agreed for a data transfer procedure: codes, operating
modes, transfer speeds and the algorithmic transfer sequence. The stipulation of the
algorithmic sequence is referred to as transfer protocol (protocol for short). A transfer
protocol generally defines the following phases of data transfer:
• Request from A to B for data interchange
• Data interchange
• End of data interchange
The transfer protocol is essentially a matter of the control. This means that it handles data
transfer independently on the basis of this protocol.
4.2.2 The 3964-R transfer protocol /1/
Unlike non-protocol-based data transfer procedures, 3964-R is a data transfer procedure
with protocol. This means that the actual data to be transferred is enclosed in specific control
characters. The 3964-R driver allows comparatively reliable data transfer by virtue of the fact
that the receiver must first signal to the transmitter that it is ready to receive (connection
set-up) and, after data interchange, must acknowledge correct reception. Data integrity is
enhanced by an additional block check character with the 3964-R transfer protocol.
The 3964-R driver interprets the following control characters:
• DLE (10
hex
) Data Link Escape
• STX (02
hex
) Start of Text
• NAK (15
hex
) Negative Acknowledgement
• ETX (03
hex
) End of Text
With the 3964-R transfer protocol, a block check character (BCC for short) is transmitted
for data integrity at the end of each data block. The block check character BCC is the even
longitudinal parity (EXORing of all data Bytes) of a transmitted or received block.
Generation starts with the first user data Byte (first Byte of the telegram) after connection
set-up and ends after characters DLE and ETX on connection cleardown.