HI-8685 Ver la hoja de datos (PDF) - Holt Integrated Circuits
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HI-8685
Holt Integrated Circuits
HI-8685 Datasheet PDF : 11 Pages
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HI-8685, HI-8686
FUNCTIONAL DESCRIPTION (cont.)
ERROR CHECKING
Once a word gap is detected, the data word in the input
register is transferred to the receive buffer and checked
for errors.
Read Byte Data Bus Bits
ARINC Bits
1st Byte 1
2nd Byte 2
D0 - D15
D0 - D15
ARINC 1 - ARINC 16
ARINC 17 - ARINC 32
When parity detection is enabled (PARITY ENB high), the
received word is checked for odd parity. If there is a parity
error, the 32nd bit of the received data word is set high.
If parity checking is disabled (PARITY ENB low) the 32nd
bit of the data word is always the 32nd ARINC bit re-
ceived.
The ERROR flag output is set high upon receipt of a word
gap and the number of bits received since the previous
word gap is less than or greater than 32. The ERROR flag
is reset low when the next valid ARINC word is written into
the receive buffer or when RESET is pulsed low.
READING RECEIVE BUFFER
When the data word is transferred to the receive buffer,
the DATA RDY pin goes high. The data word can then be
read in two 16-bit bytes by pulsing the READ input low as
indicated in Figure 5. The first read cycle resets
DATARDY low and increments an internal counter to the
second 16-bit byte. The relationship between each bit of
an ARINC word received and each bit of the two 16-bit
data bus bytes is specified in Figure 2.
When a new ARINC word is received it always overwrites
the receive buffer. If the first byte of the previous word
has not been read, then previous data is lost and the
receive buffer will contain the new ARINC word. How-
ever, if the DATARDY pin goes high between the reading
of the first and second bytes, the first byte is no longer
valid because the corresponding second byte has been
overwritten by the new ARINC word. Also, the next read
will be of the first byte of the new ARINC word since the
internal byte counter is always reset to the first byte when
new data is transferred to the receive buffer.
FIGURE 2. ORDER OF RECEIVED DATA
RESET
A low on the RESET input sets a flip-flop which initializes
the internal logic. When RESET goes high, the internal
logic remains in the initialized state until the first word gap
is detected preventing reception of a partial word.
TEST MODE
The built-in differential line receiver can be disabled allow-
ing the data and clock detection circuitry to be driven di-
rectly with digital signals. The logical OR function of the
TESTA and TESTB is defined in Truth Table 1. The two in-
puts can be used for testing the receiver logic and for input-
ting ARINC 429 type data derived from another source / pro-
tocol. See Figure 4 for typical test input timing.
The device should always be initialized with RESET imme-
diately after entering the test mode to clear a partial word
that may have been received since the last word gap. Oth-
erwise, an ERROR condition may occur and the first 32 bits
of data on the test inputs may not be properly received.
Also, when entering the test mode, both TESTA and
TESTB should be set high and held in that state for at least
one word gap period (17 gap clocks) after RESET goes
high.
When exiting the test mode, both test inputs should be held
low and the device initialized with RESET.
RINA (-10)
-1.50V to +1.50V
-3.25V to -6.50V
+3.25V to +6.50V
X
X
X
X = don't care
TRUTH TABLE 1.
RINB (-10)
TESTA TESTB
-1.50V to +1.50V
0
0
+3.25V to +6.50V
0
0
-3.25V to -6.50V
0
0
X
0
1
X
1
0
X
1
1
RXA
0
0
1
0
1
0
HOLT INTEGRATED CIRCUITS
4
RXB
0
1
0
1
0
0
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