mc145428dw Lansdale Semiconductor, Inc., mc145428dw Datasheet - Page 7

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mc145428dw

Manufacturer Part Number
mc145428dw
Description
Asynchronous?to?synchronous And Synchronous?to? Asynchronous Converter
Manufacturer
Lansdale Semiconductor, Inc.
Datasheet
ML145428
are loaded into the SYNCHRONOUS CHANNEL TRANS-
MITTER and are sent using a special zero insertion technique.
When stripped data is being transmitted, the synchronous data
transmitter will insert a binary 0 after any succession of five
continuous 1’s of data. Therefore, using this technique, no pat-
tern of (01111110) or (11111110) can occur while sending
data. This also allows the DSI to synchronize itself to the
incoming synchronous data word boundaries based on the data
alone.
er) performs the reverse operation by removing a binary 0 that
follows five continuous 1’s in order to recover the transmitted
data. (note that a binary 1 which follows five continuous 1’s is
not removed so that flags and breaks may be detected.) Figure
2B shows an example of this process.
Page 7 of 14
When stripped data words reach the top of the Tx FIFO they
The receive section of the DSI (synchronous channel receiv-
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is output at DCO, the FIFO will fill. The TxS pin will go low
when the FIFO contains two or more words. TxS may, there-
fore, be used as a local Clear-to-Send control line at the asyn-
chronous interface port to avoid transmit data over-runs.
continuous stream of data the DSI’s synchronous channel
transmitter will insert a flag synchronnizing word (01111110)
every 61st data word. The DSI’s synchronous channel receiver
checks for this synchronizing word and if not present, the loss
of synchronizaion will be indicated by the RxS pin being
latched low until the flag synchronizing word is received. Note
that under these conditions the data will continue to output at
RxD.
RECEIVE CIRCUIT
the ML145428 at the DCI pin under the control of the DC and
DIE pins (see SYNCHRONOUS CHANNEL INTERFACE
section). Framing information, break code detection, and data
word recovery functions are performed by the SYNCHRO-
NOUS CHANNEL RECEIVER. Recovered data words are
loaded into the four word deep Rx FIFO. When the recovered
data words reach the top of the Rx FIFO they are taken by the
DATA FORMATTER, start and stop bits are re-inserted and
the re-constructed asynchronous data is output at the TxD pin
at the same baud rate as the transmit side. The number of stop
bits and word length are those selected by the SB and DL pins.
going low. Data will continue to be output under these condi-
tions, but RxS will remain low until frame synchronization,
i.e., the detection of a framing flag word, is re-established. If
the output data rate is less than the data rate of the incoming
synchronous data channel, data will be lost at the rate of one
word at a time due to the bottom word on the Rx FIFO being
overwritten. In order to prevent data loss (in the form of asyn-
chronous terminal to asynchronous terminal over-runs) due to
clock slip between remote DSI links, (during long bursts the
stop bit which it re-creates at its RxD output by 1/32nd. This
action allows the originator of a transmission (of asynchronous
data) to be up to 3% faster than the receive device is expecting
for any given data rate. This tolerance is well with in the nor-
mally expected differences in clock frequencies between
remote stations. If the Rx FIFO is overwriting the RxS line
will pulse low for one DC clock period following the over-
writing of the bottom level of the Rx FIFO.
INITIALIZATION
When held low, the internal FIFOs are cleared, the TxD input
appears high to the data strippers, internal circuitry. DCO is
forced to a high impedance state, TxS and RxS are forced low.
When brought high normal operation resumes and and the syn-
chronous channel transmitter sends the flag code until data has
reached the top of the Tx FIFO. Note that the TxS line will
immediately go high after RESET goes high, while RxS will
remain low until framing is detected. The synchronous channel
If the incoming data rate at TxD exceeds the rate at which it
In order to insure synchronization during the transfer of a
Data incoming from the synchronous channel is loaded into
Loss of framing, if it occurs, is indicated by the RxS pin
Initialization is accomplished by use of the RESET pin.
LANSDALE Semiconductor, Inc.
Issue 0

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