User's Manual

SYSTEM DESCRIPTION, INSTALLATION, AND MAINTENANCE MANUAL
eNfusion® HSD-440 Mark 2 Terminal
23-15-30 F-7
3 JUN 10
4. Understanding LDUs and File Size
BOP messages use Link Data Units (LDUs) encoded in binary octets to transmit data. LDUs
conform to the following rules:
• The data is transmitted from a source and is received by a sink.
• LDUs consist of a set of contiguous ARINC 429 32 bit data words.
• The initial data word of each LDU shall b
e a Start of Transmission (SOT) word.
• The end data word of each LDU shall be an End of Transmission (EOT).
• No data file shall exceed 255 LDUs.
5. Understanding LDU Size and Word Count
LDUs may vary in size from 3 to 255 ARINC 429 words. The minimum LDU consists of one
SOT word, one data word, and one EOT word, and the maximum LDU consists of one SOT,
253 data words, and one EOT.
The HSD-440 Mark 2 Terminal calculates word co
unt when it organizes an LDU for transmission.
The word count appears in the RTS and CTS data words. See "Understanding Protocol Words"
on page F-9.
6. Understanding Word Format
The general word format of a BOP word is given in ARINC 429 (Attachment 11, Table 11-A).
The bit definitions are shown in Table F-6.
Table F-6 BOP Word Format
Bit Position Description
8-1 SAL
24-9 Data (28-9 for full data words)
28-25 GFI, control data or word type extensions
31-29 Word type
32 Parity bit
A. Understanding SALs
The HSD-440 Mark 2 Terminal sends LDUs by point to point by using a label field to carry
the d
estination SAL; therefore, each LDU that the HSD-440 Mark 2 Terminal sends is
prefixed by the SAL for the CMU, SAL 304.
The SAL for the HSD-440 Mark 2 Terminal is 307
(if designated SDU 1) or 173 (if
designated SDU 2). See ARINC 429, Part 1, attachment 1-1 for a complete list of all SALs.
B. Understanding Data
Data is sent in 4 or 5 nib
ble words. See "Understanding Word Types" on page F-8