HI-8783, HI-8784, HI-8785

The HI-8784 and HI-8785 have the same digital logic func-

tion as the HI-8783, but include an on-chip line driver de-

signed to directly drive the ARINC 429 bus. The two ARINC

outputs (TXAOUT and TXBOUT) provide a differential volt-

age to produce a +10 volt One, a -10 volt Zero, and a 0 volt

Null. The slope of the ARINC outputs is controlled by the

SLP1.5 pin. If SLP1.5 is high, the output rise and fall time is

nominally 1.5us. If SLP1.5 is set low, the rise and fall times

are 10us. DATA ONE and DATA ZERO outputs are not pro-

vided for the HI-8784 and HI-8785.

The HI-8784 has 37.5 ohms in series with each line driver out-

put. The HI-8785 has 10.0 ohms in series. The HI-8785 is for

applications where external series resistance is needed, typi-

cally for lightning protection devices.

FUNCTIONAL DESCRIPTION (Cont.)

A0

Byte

Data Bus

ARINC Bits

1

Byte 1

D0 - D7

ARINC 1 - ARINC 8

0

Byte 2

D0 - D7

ARINC 9 - ARINC 16

0

Byte 3

D0 - D7

ARINC 17 - ARINC 24

0

Byte 4

D0 - D7

ARINC 25 - ARINC 32

Figure 2. Order of transmitted bytes

Figure 1. Block Diagram

DATA

BUS

8to32bit

mux

32 bit

buffer

register

32 bit

shift

register

byte

counter

WRITE

A0

8

32

32

status &

control

logic

XMT RDY

XMIT CLK

word gap

counter

bit

counter

output

logic

line

driver

PARITY ENB

DATA ZERO

DATA ONE

561 DATA

561 SYNC

TXBOUT

TXAOUT

SLP1.5

HI-8784, HI8785

HI-8783

POWER SUPPLY SEQUENCING

The power supplies must be controlled to prevent large

currents during supply turn-on and turn-off. The required

sequence is V+ followed by VDD, always ensuring that V+ is

the most positive supply. The V- supply is not critical and can

be asserted at any time.

HOLT INTEGRATED CIRCUITS

3