HI-3593
FUNCTIONAL DESCRIPTION (cont.)
RECEIVED ARINC 429 WORD
TO FILTERS (S/D, LABEL, PRIORITY-LABEL)
DATA
PARITY
CHECK
32 BIT SHIFT REGISTER
WORD
GAP
WORD GAP
TIMER
ONES
NULL
SHIFT REGISTER
SHIFT REGISTER
SHIFT REGISTER
EOS
END
BIT
CLOCK
NEW WORD
BIT
COUNTER
AND
END OF
1MHz
SEQUENCE
CONTROL
32ND
BIT
START
SEQUENCE
1MHz
1MHz
ZEROS
ERROR
ERROR
DETECTION
1MHz
FIGURE 3. RECEIVER BLOCK DIAGRAM
RECEIVE DATA FIFO
RETRIEVING DATA
Each time a valid ARINC 429 word is loaded into the FIFO, the
Receive FIFO Status Register FFEMPTY, FFHALF and FFFULL bits
are updated. When the FIFO is EMPTY, the FFEMPTY bit is a “1” and
FFHALF and FFFULL are “0”. Once the first received and accepted
ARINC 429 word is loaded into the FIFO, FFEMPTY goes low. Each
receivedARINC 429 word is retrieved via the SPI interface using SPI
Op-Code 0xA0 (Receiver 1) or 0xC0 (Receiver 2).
Following S/D Filtering, accepted ARINC 429 words are
conditionally stored in the Receive FIFO. If label filtering is
disabled, all words are stored. If label filtering is enabled, the
incoming ARINC429 word’s label byte value is checked against its
corresponding bit in the pre-programmed label look-up table. If the
bit is set to a “1” the word is stored in the FIFO. If the bit is a “0” the
word is not stored in the FIFO.
Up to 32 ARINC 429 words may be held in the Receive FIFO.
FFFULL goes high when the Receive FIFO is full. Failure to unload
the Receive FIFO when full causes additional valid ARINC 429
words to overwrite Receive FIFO location 32.
LABEL RECOGNITION
The user loads the 256-bit label look-up table to specify which 8-bit
incoming ARINC labels are stored in the Receive FIFO, and which
are not. Setting a “1” in the look-up table enables processing of
received ARINC words containing the corresponding label. A “0”
in the look-up table causes discard of received ARINC words
containing the label. The 256-bit look-up table is loaded using SPI
Op-Codes 0x14 (Receiver 1) and 0x28 (Receiver 2), as described
in Table 1. After the look-up table is initialized, the Control Register
bit LABREC must be set to enable label recognition.
A FIFO half-full flag (FFHALF) is high whenever the Receive FIFO
contains 16 or more words. The FFHALF bit provides a useful
indicator to the host CPU that a sixteen word data retrieval routine
may be performed.
The FFEMPTY, FFHALF or FFFULLstatus bits can also be output on
the R1FLAG (Receiver 1) and R2FLAG (Receiver 2) pins. Flag /
Interrupt Assignment Register bits 5, 4, 1 and 0 select which flag
appears. Additionally, a FIFO not empty option may be programmed
for the R1FLAG / R2FLAG pins causing the pin to go high any time at
least one word is available in the FIFO.
All four bytes of the incoming ARINC429 word are stored in the
FIFO.
Table 3. defines the rules for Receive FIFO loading.
READING THE LABELLOOK-UPTABLE
The contents of the Label Look-up table may be read via the SPI
interface using Op-Code 0x98 (Receiver 1) or 0xB8 (Receiver 2) as
described inTable 1.
HOLT INTEGRATED CIRCUITS
11
HOLTIC [ HOLT INTEGRATED CIRCUITS ]
