EUCHNER Electronic-Key Adapter with serial Interface - Manual (Page 16)

Manual EKS Electronic-Key Adapter serial
088796-02-03/05 Subject to technical modifications Page 16/24
8.3.1 Special features of the 3964R data transfer protocol [1]
The 3964R data transfer protocol is a comparatively reliable protocol for the electronic exchange of data
between PC/control system and a peripheral connected, because the data transfer is performed using a
standardized protocol.
On control systems with an integrated 3964R driver (see e. g. [1] ) it is not necessary for the user to become
involved in the details of setting up the connection and data integrity. Here it is sufficient to use the program to
pass the message core to the 3964R driver.
However, on control systems without a 3964R driver or on the connection of the Electronic-Key adapter to the
PC, the user must also program the connection setup as well as retries and DLE duplication.
Integration of the Electronic-Key adapter with serial interface into the user’s PC application is supported by an
optionally available ActiveX module (order no. 084 708) (usable if user programs on MS Windows® support
ActiveX). EKS can thus be used in conjunction with process visualization.
8.3.1.1 Basic information on data transfer procedures using a protocol [1]
Numerous conventions must be agreed for a data transfer procedure; codes, operating modes, transfer speeds
and the algorithmic process for the transfer. The definition of this algorithmic process is termed the transfer
protocol (for short: protocol).
A transfer protocol in general defines the following phases of the data transfer:
Connection setup: request from A to B for the transfer of data
Data transfer from A to B
Connection termination: conclusion of the transfer of data
8.3.1.2 The 3964R transfer protocol [1]
Unlike protocol-free data transfer procedures, 3964R is a data transfer with protocol. This means that the actual
data that need to be transferred are enclosed in specific control characters. The 3964R driver permits
comparatively reliable data transfer as the recipient must signal to the sender readiness to receive (connection
setup) and acknowledge correct reception after completion of the data transfer. With the 3964R transfer
protocol, data integrity is increased by an additional block check character.
The 3964R 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
At the end of each data block in the 3964R transfer protocol, a block check character (for short: BCC) is sent
to assure data integrity. The block check character is the even longitudinal parity (XOR operator on all data
bytes) of a block sent or received. The block check character is formed starting with the first byte of the
message core after the connection is setup and ends after the characters DLE and ETX during connection
termination.
8.3.1.3 The control system sends [1]
To setup the connection, the control system sends the control character STX. If, before the acknowledgement
delay time (ADT, typically: 2 s) elapses the peripheral responds with the control character DLE, the control
system switches to transfer mode. If the peripheral responds with the control character NAK, any other
character (except DLE) or the acknowledgement delay time elapses without a reaction, the attempt to setup the
connection has failed. After a total of 6 unsuccessful attempts (3964R protocol specification) the process is
aborted. If the attempt to setup the connection is successful, the characters with the information as contained in
the send buffer in the control system are transferred to the peripheral at the selected transfer speed.