Manual EKS Electronic-Key Adapter USB
2094485-05-07/19
Subject to technical modifications
Page 27/34
8.3 Basic message structure
Every command and any related data blocks are transferred from and to the device 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 acknowledgment
character (DLE). If the acknowledgment 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
Acknowledg
ment from
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 data
items
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 connected peripheral device, because 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 data transfer:
Connection setup: request from A to B for data transfer
Data transfer from A to B
Connection termination: conclusion of data transfer