User's Manual

SYSTEM DESCRIPTION, INSTALLATION, AND MAINTENANCE MANUAL
eNfusion® HSD-440 Mark 2 Terminal
23-15-30 F-11
3 JUN 10
E. Understanding Start of Transmission (SOT)
When the HSD-440 Mark 2 Terminal receives a valid CTS with the destination code and
word count of the previous RTS, then it responds by sending an SOT word immediately
before the LDU. The SOT contains the file sequence number, the GFI, and the LDU
sequence number.
The file sequence number (bits 24–17) of the SOT word is an 8 bit number assigned to
the data file. It is initialized to 00h and increments by 1h for each new file sent over the
link. After reaching FFh, the file sequence number returns to 01h and recommences
incrementing by 1h for each new file sent. A file consisting of multiple LDUs has the same
file sequence number in each SOT word of each LDU. The file sequence number is also
used in ACK and NAK words.
The LDU sequence number (bits 16–9) of the SOT word is an 8 Bit number assigned to
the LDU. It is initialized to 00h and increments by 1h for each LDU sent (of the same file).
The LDU sequence number resets to 00h at the beginning of each new file. The LDU
sequence number is also used in the ACK word.
F. Understanding End of Transmission (EOT)
Each LDU is terminated by an EOT word. Bit 25 indicates if this LDU is the final LDU of
the transfer. If it is, then this bit shall be set to 1; if it is not the final LDU, it shall be set to
0. The EOT also contains the CRC word in bits 24–9. See ARINC 429 P3, paragraph
2.5.12, for details on generating and decoding the CRC word.
Loop 0001b 16 Bit Loop Back
Solo Word ID 16 Bit Data Filed
Table F-10 Data Types (Continued)