HD-6408 Datasheet, PDF (5/11 Pages) Intersil Corporation – CMOS Asynchronous Serial Manchester Adapter (ASMA)

HD-6408
Decoder Operation
The Decoder requires a single clock with a frequency of 12
times the desired data rate applied at the DClock input. The
Manchester II coded data can be presented to the Decoder
in one of two ways. The BOI and BZI inputs will accept data
from a differential output comparator. The UDI input can only
accept noninverted Manchester II coded data (e.g. from
BOO of an Encoder through an inverter to UDI).
The Decoder is free running and continuously monitors its
data input lines for a valid sync character and two valid
Manchester data bits to start an output cycle. When a valid
sync is recognized (1), the type of sync is indicated by the
CDS output. If the sync character was a command, this out-
put will go high (2) and remain high for sixteen DSC periods
(3), otherwise it will remain low. The TD output will go high
and remain high (2) - (3) while the Decoder is transmitting
the decoded data through SDO.
The decoded data available at SDO is in a NRZ format. The
DSC is provided so that the decoded bits can be shifted into
an external register on every low-to-high transition of this
clock (2) - (3). Note that DECODER SHIFT CLOCK may
adjust its phase up until the time that TAKE DATA goes high.
After all sixteen decoded bits have been transmitted (3) the
data is checked for odd parity. A high on VW output (4) indi-
cates a successful reception of a word without any
Manchester or parity errors. At this time the Decoder is look-
ing for a new sync character to start another output
sequence. VALID WORD will go low approximately 20
DECODER SHIFT CLOCK periods after it goes high if not
reset low sooner by a valid sync and two valid Manchester
bits as shown (1).
At any time in the above sequence a high input on DR during
a low-to-high transition of DSC will abort transmission and ini-
tialize the Decoder to start looking for a new sync character.
TIMING
DSC
BOI
BZI
TD
CDS
SDO
VW
0
1
2
3
4
5
6
7
8
1ST HALF 2ND HALF 15 14 13 12 11 10
SYNC SYNC 15 14 13 12 11 10
UNDEFINED
FROM PREVIOUS RECEPTION
15 14 13 12
12
16 17 18 19
2
1
0P
2
1
0P
4
3
2
1
0
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