User`s guide

4: FMP Link Configuration Options
DC 900-1339H 87
4.13.4 Data Records with Header
On inbound messages with Message Blocking set to Data Records with Header, FMP
strips out block check characters and all control characters including unit separators.
Each individual record is preceded by a 5-byte header that contains information about
the record. Figure 4–12 shows the format of the record header. The first two bytes con-
tain a 16-bit count of the number of record bytes that follow it (including the rest of the
record header). The next two bytes contain a 16-bit FMP-generated block sequence
number. If multiple records are received in the same block, they will have the same
sequence number. The last header byte contains an 8-bit error code pertaining to that
record (see Appendix C for the error code values). If the record contains no errors, this
field is zero. If a BCC error or other receive error is detected within the record, an error
code is placed in this field. Figure 4–13 is an example of the Data Records with Header
setting using the sample received data blocks shown in Figure 4–6 on page 82.
On outbound messages, the client application places individual records in the write
buffer separated by US characters (as in the Data Records setting). The FMP software
adds all the BSC control characters necessary to send the records in one block. In addi-
tion, FMP generates the block check character for each record. No header is required on
outbound messages. See Figure 4–10 on page 85 for an example of transmitted data for
this setting.
Figure 4–12: Example of a User’s Transparent Inbound Message
PAD SYN SYN SYN DLE SOH data DLE ETX BCC PAD
Message as received by FMP
count sequence number error data (DLI_PROT_RECV_PACKED_DATA_EOM)
User’s inbound message from FMP
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