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S5-95F
Receive Coordination Via the User Valid Byte (as per the Parameter Values Initialized with
COM 95F)
You cannot process the Receive Mailbox until the operating system has completed the data
transfer. To ascertain the status of the data transfer, you can evaluate the User Valid Byte.
User Valid Byte
7
6
5
4
3
User Program for Receiving Data
The user program for receiving data should have the following structure:
Check to see if a frame has been received.
Bit 1 or bit 3 in the UVB are "0".
Set bit 1 or bit 3 in the UVB to inform the operating system that you are ready to receive the
next frame.
When the operating system resets bit 1 or bit 3, read the Receive Mailbox. Evaluate
- DL 0 (number of net data bytes received)
- DR 0 (condition code byte for Receive)
- DW 1 and subsequent data words (net data)
After you have evaluated this data, set bit 0 or bit 3 to inform the operating system that you are
ready to receive the next frame.
EWA 4NEB 812 6210-02
2
1
0
0: Program can process Receive Mailbox (data path 1) in
DB 252.
1: Program is waiting for next useful data frame; the
operating system will reset this bit as soon as the next
useful data frame has been transferred without error.
0: Program can process Receive Mailbox (data path 2) in
DB 253.
1: Program is waiting for next useful data frame; the
operating system will reset this bit as soon as the next
useful data frame has been transferred without error.
S5-95F on SINEC L1
13-21
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