
TRANSMITTER
AblockdiagramofthetransmittersectionisshowninFigure3.
TheFIFOisloadedsequentiallybyfirstpulsing
andthen
toloadbyte2. Thecontrollogicautomaticallyloads
the 31 bit word in the next available position of the FIFO. If TX/R,
the transmitter ready flag is high (FIFO empty), then 8 words,
each 31 bits long, may be loaded. If TX/R is low, then only the
available positions may be loaded. If all 8 positions are full, the
FIFOignoresfurtherattemptstoloaddata.
toloadbyte1
When ENTX goes high, enabling transmission, the FIFO
positions are incremented with the top register loading into the
data transmission shift register. Within 2.5 data clocks the first
data bit appears at either 429DO or
data transmission shift register are presented sequentially to the
outputsintheARINC429formatwiththefollowingtiming:
. The 31 bits in the
429DO
ARINC DATA BIT TIME
DATA BIT TIME
NULL BIT TIME
WORD GAP TIME
10 Clocks
5 Clocks
5 Clocks
40 Clocks
80 Clocks
40 Clocks
40 Clocks
320 Clocks
The word counter detects when all loaded positions are
transmittedandsetsthetransmitterreadyflag,TX/R,high.
FIFOOPERATION
DATATRANSMISSION
PL1
PL2
HIGHSPEED
LOWSPEED
TRANSMITTER PARITY
The parity generator counts the ONES in the 31-bit word. If the
BD12 control word bit is set low, the 32nd bit transmitted will
make parity odd. If the control bit is high, the parity is even.
If the BD05 control word bit is set low, 429DO or
inputs to the receiver bypassing the interface circuitry.
become
The two receivers are independent of the transmitter. Therefore,
control of data exchanges is strictly at the option of the user. The
only restrictions are:
1. The received data may be overwritten if not retrieved
withinoneARINCwordcycle.
2. The FIFO can store 8 words maximum and ignores
attemptstoloadadditiondataiffull.
3. Byte1ofthetransmitterdatamustbeloadedfirst.
4. Either byte of the received data may be retrieved first.
Bothbytesmustberetrievedtoclearthedatareadyflag.
5. After ENTX, transmission enable, goes high it cannot go
low until TX/R, transmitter ready flag, goes high. Otherwise,
oneARINCwordislostduringtransmission.
SELF TEST
SYSTEM OPERATION
429DO
HI-8581
HOLT INTEGRATED CIRCUITS
5