Encoder Operation
The Encoder requires a single clock with a
frequency of twice the desired data rate applied
at the SEND CLOCK input. An auxiliary
divide by six counter is provided on chip which
can be utilised to produce the SEND CLOCK
by dividing the DECODER CLOCK.
The Encoder's cycle begins when
ENCODER ENABLE is high during a failing
edge of ENCODER SHIFT CLOCK
x
. This
cycle lasts for one word length or twenty
ENCODER SHIFT CLOCK periods. At the
next low-to-high transition of the ENCODER
SHIFT CLOCK, a high at SYNC SELECT
input actuates a command sync or a low will
produce a data sync for that word
y
. When the
Encoder is ready to accept data, the SEND
DATA output will go high and remain high for
sixteen ENCODER SHIFT CLOCK periods
z
.
During these sixteen periods the data should be
clocked into the SERIAL DATA input with
every low-high transition of the ENCODER
SHIFT CLOCK
z
-
{
. After the sync and the
Manchester II coded data are chip transmitted
through the BIPOLAR ONE and BIPOLAR
ZERO outputs, the Encoder adds on an
additional bit which is the parity for that word
|
. At any time a low in OUTPUT INHIBIT
input will force both bipolar outputs to a high
state but will not affect the Encoder in any other
way. To abort the Encoder transmission a
positive pulse must be applied at MASTER
RESET. Anytime after or during this pulse, a
low to high transition on SEND CLOCK clears
the internal counters and initializes the Encoder
for a new word.
Timing
0 1
2
3
4
5
6
7
15 16 17 18 19
Send Clock
Encoder
Shift Clock
Encoder
Enable
Don’t Care
Sync Select
Valid
Don’t Care
Send Data
Serial Data In
Bipolar
One Out
15 14 13 12 11 10
3 2
1
0
1st
2nd
15 14 13 12 11
3
2
1
0
P
Half Half
Bipolar
Zero Out
Sync Sync
15 14 13 12 11
3
2
1
0
P
1
2
3
4
5
Figure 9: Encoder Operation
Aeroflex Circuit Technology
6
SCD15530 REV B 7/28/99 Plainview NY (516) 694-6700
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
