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06.91
3.3
Procedures
3.3.1
3964R procedure
The 3964R procedure processes all operations necessary to control the data flow between the
CP 315 interface module and the connected node (e.g. computer).
The 3964R procedure is an asynchronous, bit-serial transmission method. Transmit and
receive clock (baud rate) must be set to the same value on the CP 315 interface module and
in the connected peripheral unit since no clock cable is provided between the two devices
(asynchronous). Control characters and useful information characters are transmitted through
the junctions.
When addressing an interface of the CP 315, to which a computer link section is connected,
the computer link program modules in the CP 315 are activated.
Two or more units of an identical or different type can be connected with each other. Each
interface of the basic board and of the expansion board can be assigned to one computer link
channel.
A message frame sequence is shown below in a global manner between two nodes which are
connected with each other over a point-to-point connection. A more detailed description is
given on the following pages.
•
Output commands - data from node I to node II
Node I
Message frame header + data
Response message
Subsequent message frame
Subsequent response message
In the case of large data volumes which cannot be transported in one message frame a
subsequent message frame is sent.
The block length of the message frame is configurable. Block lengths between 128 and 256
characters are possible.
Transmitting using the 3964R procedure
(CP 315 acting as transmitter = active CP 315)
To establish the connection, the 3964R procedure sends the STX control character (request to
send). If the peripheral unit responds within the timeout period with the DLE character, the
procedure switches to the transmit mode. If the peripheral unit responds with NAK, any other
character (except DLE) or a mutilated character, or if the timeout period elapses without a
response, the connection establishment attempt has failed. The driver then attempts again to
establish the connection. After failed repeated attempts, the number of which is configurable,
the driver aborts the process and enters an error message in the exception trace.
© Siemens AG 1989 All Rights Reserved
SINUMERIK 840/880 (PJ)
Node II
6FC5 197-0AB20-0BP0
3 Interface Modules
3.3 Procedure
3–15
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