EUCHNER EKS FSA with USB Interface - Manual (Page 37)

Manual EKS Electronic-Key Adapter USB
094485-04-11/13 Subject to technical modifications Page 37/44
8.3 Basic message structure
Every command and any related data blocks are transferred from and to the Electronic-Key adapter in a
message core within the message frame as per the protocol 3964R (Figure 1: Basic command structure in the
3964R protocol).
In the 3964R protocol, the recipient acknowledges the message received by sending back an acknowledgement
character (DLE). If the acknowledgement is negative (NAK), the complete protocol is repeated. If it is not
possible to correctly transfer the protocol after a total of six attempts, the process is aborted.
Description Byte no.
Transmit data
in ASCII format
Acknowledge-
ment from
the recipient
+ -
Connection setup 3964R procedure start STX
DLE NAK
Message core Number of message bytes 0
Command identification
1
2 T or R
command
Device address 3 01
hex
User data description
4
5
6
Start address
Start address
Number of items of
data
User data 7 ... n
Connection termination
3964R procedure termination
DLE
ETX
BCC
DLE NAK
Figure 1: Basic command structure in the 3964R protocol
8.3.1 Special features of the 3964R data transfer protocol [1]
The 3964R data transfer protocol is a comparatively reliable procedure for the electronic exchange of data
between PC/control system and a peripheral connected, because the data transfer is performed using a
standardized protocol.
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