EUCHNER Electronic-Key Adapter with serial Interface - Manual (Page 17)

Manual EKS Electronic-Key Adapter serial
088796-02-03/05 Subject to technical modifications Page 17/24
The peripheral monitors the amount of time between the incoming characters. The gap between two characters
must not be more than the character delay time (CDT, typically: 100 ms).
All 10
hex
values contained in the message core must be sent twice so that the recipient recognizes that here
information is being transferred and not the control character DLE (DLE duplication).
After the data has been sent, the control system adds the following characters as an end identifier: DLE ETX
BCC.
Then the control system waits for an acknowledgement character from the peripheral. If the peripheral sends
the control character DLE within the acknowledgement delay time (ADT, typically: 2 s), the data block has been
received correctly. If, on the other hand, the peripheral responds with the control character NAK, any other
character or the acknowledgement delay time elapses without a reaction, the control system starts again from
the beginning by setting up a connection with STX. After a total of 6 unsuccessful attempts (3964R protocol
specification) to send the data block, the process is aborted and the control system sends the control character
NAK to the peripheral.
8.3.1.4 The control system receives [1]
If the control system receives the control character STX from the peripheral when the control system is idle, it
responds with DLE. If the control system receives another character (except STX) when it is idle, it waits until
the character delay time (CDT, typically: 100 ms) has elapsed and then sends the control character NAK.
After each character, the next character is awaited during the character delay time (CDT). If the character delay
time elapses without the reception of a character, the control character NAK is sent to the peripheral.
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 6 attempts (3964R protocol specification) or the retry
is not started by the peripheral within the block waiting time of 4 s, the control system aborts 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 as a character in the information to be transferred, on the occurrence of a 10
hex
value in the information to be transferred, a 10
hex
value must be sent again. This means that if a byte
with the 10
hex
value occurs in the message core, this character must be transferred again so that it is not
interpreted by the receiving end as the control character DLE for terminating the connection.
The block check character (BCC):
At the end of each data block, a block check character 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.
Retries on errors:
If an error occurs for any reason during the data transfer, a total of 6 attempts are made to transfer the
data correctly.