Appendix; Reception Using The 3964R Procedure - Siemens SINUMERIK 840 Planning Manual

08.89
9

Appendix

9.1

Reception using the 3964R procedure

(CP315 as receiver = passive CP315)
The receiver waits in idle state for the connection being established by the peripheral unit.
When the driver is ready to receive and the STX character is received, a DLE response is
given and the driver is switched to receive mode.
Then following receiving characters are stored in the input buffer. If two consecutive DLE
characters are received, these are loaded into the input buffer as one DLE character only.
Reception of the incoming characters is monitored using the character delay period. If the
character delay period elapses without a character being received, the NAK character is sent
to the peripheral unit.
When recognizing the character sequence DLE, ETX and BCC, the driver terminates
reception, loads ETX as end character into the buffer (DLE is suppressed) and sends DLE to
the peripheral unit to indicate an error-free (or NAK for a block containing errors) received
block. Data exchange is thus ended. The driver returns into the passive state.
If the driver status is unclear upon receipt of STX (e.g. contents of input buffer not yet
retrieved), the driver sends NAK to the peripheral unit.
If during reception a break condition on the input line occurs, or the character delay period is
exceeded or a buffer overflow occurs (>128 characters), the receiving driver aborts reception,
sends NAK and returns to the passive state.
If transmission errors occur during reception (lost character, frame error, parity error) reception
is continued, and after arrival of the DLE, ETX, BCC characters the received block is
acknowledged negatively by transmitting NAK to the peripheral unit. A repetition of the block is
then expected.
If the block cannot be received even after several attempts (value is configurable) without
error, the 3964R procedure aborts the reception and reports an error.
© Siemens AG 1989 All Rights Reserved
SINUMERIK 840/880 (PJ)
9.1 Reception using the 3964R procedure
6FC5 197-0AB20-0BP0
9 Appendix
9–1