Profichip VPC3+C - Write Read Data; Data Exchange

6 PROFIBUS DP Interface
Bit Position
Byte
7 6 5 4 3 2 1 0
Designation
0
Ext_Diag_ Overflow Stat_Diag Ext_Diag
1
2
3
4
5
6
:
n
user input
Ext_Diag_Data
(n = max. 243)
Figure 6-11: Format of the Diagnosis-Buffer
The Ext_Diag_Data must be entered into the buffers after the VPC3+C
internal diagnosis data. Three different formats are possible here: device-
related, ID-related and port-related. If PROFIBUS DP extensions shall be
used, the device-related diagnosis is substituted by alarm and status
messages. In addition to the Ext_Diag_Data, the buffer length also includes
the VPC3+C diagnosis bytes (R_Len_Diag_Buf 1, R_Len_Diag_Buf 2).
6.2.5 Write_Read_Data / Data_Exchange (Default_SAP)
Writing Outputs
The VPC3+C writes the received output data in the 'D' buffer. After an
error-free receipt, the VPC3+C shifts the newly filled buffer from ‘D’ to ‘N'.
In addition, the DX_Out interrupt is generated. The user now fetches the
current output data from ‘N’. The buffer changes from ‘N’ to ‘U’ with the
Next_Dout_Buffer_Cmd, so that the current data can be transmitted to the
application by a RD_Output request from a DP-Master.
If the user’s evaluation cycle time is shorter than the bus cycle time, the
user does not find any new buffers with the next Next_Dout_Buffer_Cmd in
‘N'. Therefore, the buffer exchange is omitted. At a 12 Mbit/s baud rate, it is
more likely, however, that the user’s evaluation cycle time is larger than the
bus cycle time. This makes new output data available in ‘N’ several times
before the user fetches the next buffer. It is guaranteed, however, that the
user receives the data last received.
For power-on, LEAVE-MASTER and the Global_Control telegram with
‘Clear_Data = 1’, the VPC3+C deletes the ‘D’ buffer and then shifts it to ‘N'.
This also takes place during power-up (entering the WAIT-PRM state). If
the user fetches this buffer, he receives U_Buffer_Cleared during the
46 Revision 1.03
VPC3+C
User Manual
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