EUCHNER EKS FSA with USB Interface - Manual (Page 39)

Manual EKS Electronic-Key Adapter USB
094485-04-11/13 Subject to technical modifications Page 39/44
When the control system detects the character string DLE ETX BCC, it ends reception. The control system
compares the block check character BCC with the longitudinal parity calculated internally. If the block check
character is correct and no other reception errors have occurred, the control system sends the control character
DLE. If the BCC is erroneous, the control character NAK is sent to the peripheral. A retry is then expected. If it
is not possible to receive the block correctly after a total of six attempts (3964R protocol specification) or the
retry is not started by the peripheral within the block waiting time of 4 s, the control system interrupts the
reception.
If transfer errors occur during reception (lost characters, frame errors, parity errors), the control system
continues to receive data until the connection is terminated and then sends the control character NAK to the
peripheral. Then a retry in the form described above is awaited.
8.3.1.5 Summary of the most important points
 DLE duplication:
For the control system to be able to differentiate between the control character DLE and a randomly
occurring 10
hex
value in the message core, a 10
hex
value in the message core must be sent twice. In this
way it is achieved that the data is interpreted by the receiving end as user data and not as control
characters for connection termination.
 The block check character (BCC):
At the end of each data block a check character is sent to assure data integrity. The block check character
BCC 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 connection is set up
and ends after the characters DLE and ETX during connection termination.
 Retries on errors:
If an error occurs for any reason during the data transfer, a total of six attempts are made to transfer the
data correctly.
8.4 Commands for writing and reading a read/write Electronic-Key
Write and read processes are always initiated by the PC using a "command message".
The Electronic-Key-System then sends a reply message to the PC.
PC/control system Electronic-Key-System
Command message
→
Reply message
←
On read/write Electronic-Keys with 116 bytes, the memory is organized in 4-byte blocks. This means a
multiple of 4-byte sized blocks must always be written.
The start address must be given in the range byte number 0 to byte number 112, always in 4-byte steps
(byte number 0, 4, 8 ... 112)!
However, during reading it is possible to access the memory byte-by-byte without the above-mentioned
restriction for writing.