Receiving With The 3964R Procedure; Link Establishment; Receiving; Initialization Conflict - Siemens SIMATIC TI505 Installation And Operation Manual

3.7

Receiving with the 3964R Procedure

Link Establishment

Receiving

Initialization
Conflict
S5 UniLink Adapter Installation and Operation
After a successful transmission of the data information has been made to
the partner, the procedure enters the idle state awaiting the link to be
established by the partner. If the procedure receives any character (except
STX) while in the idle state, it waits until the character delay time (220 ms)
has elapsed and then sends a NAK character. Then a repetition is expected.
If after a total of six unsuccessful attempts, or if the repetition by the
partner does not take place within the waiting time of 4 seconds, the
procedure breaks off reception and signals an error.
If the procedure receives the character STX it answers with DLE. The
procedure now expects a data reception from the partner.
After each character received, the procedure waits for the next character to
arrive within the character delay time (220 ms). If there is a character
timeout, the NAK character is sent to the partner, and a repetition is
expected. If after a total of six unsuccessful attempts, or if the repetition by
the partner does not take place within the waiting time of 4 seconds, the
procedure breaks off reception and signals an error.
If the procedure recognizes the character sequence DLE ETX and BCC, it
stops receiving. It compares the received block check character (BCC) with
longitudinal parity. If the block check character is correct and no other
errors have occurred during reception, the procedure sends a DLE. If the
BCC does not correspond, NAK is sent to the partner. Then a repetition is
expected. If the block can not be received without errors following six
attempts or if the repetition by the partner does not take place within the
waiting time of 4 seconds, the procedure breaks off and signals an error.
If transmission errors occurs during the reception (characters lost, frame
error, parity error), reception is continued until the link is terminated and
then NAK is sent to the partner. Then a repetition is expected as previously
described.
If a device receives a send request (STX character) from its partner and does
not answer within the acknowledgment delay time (2000 ms) with DLE or
NAK, but also sends the character STX, there is an initialization conflict.
Both devices are attempting to perform a send job. The device with the
lower priority desists and answers with the DLE character. The device with
the higher priority sends its data as previously described. After the link has
been terminated, the lower priority device can then run its send job. The S5
UniLink Adapter will assume higher priority, and the CP module should be
configured with the lower priority.
The CP module will act on a request/response basis, with all requests
coming from the S5 UniLink Adapter. Thus the S5 PLC should be
programmed never to send any requests through the CP module to the
UniLink Adapter. If such a request occurs, the S5 UniLink Adapter will
ignore the request, causing a timeout to occur.
TIWAY I Network Communication 3-11