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參數(shù)資料
| 型號： | LM1893 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LM1893/LM2893 Carrier-Current Transceiver |
| 中文描述： | LM1893/LM2893載波電流收發(fā)器 |
| 文件頁數(shù)： | 19/24頁 |
| 文件大小： | 576K |
| 代理商： | LM1893 |
Communication and System
Protocols
(Continued)
carrier current applications since they do not have the intelli-
gence needed to distinguish between real messages and
noise induced phantoms.
The difficulty in designing special protocols arises out of the
special nature of the AC line, an environment laden with the
worst imaginable noise conditions. The relatively low data
rates possible over the AC line (typically less than 9600
baud) make it even more imperative that systems utilize the
most sophisticated means available to ensure network effi-
ciency.
With these facts in mind, the designer is referred to a publi-
cation intended to aid in the development of carrier current
systems. This is literature
Y
570075 The Bi-Line Carrier Cur-
rent Networking System, a 200 pp. book that functions as
the ‘‘bible’’ of Bi-Line system design. It has sections on
LM1893 circuit optimization, protocol design, evaluation kit
usage, critical component selection, and the Datachecker/
DTS case study.
Basic Data Encoding
(please refer to the pre-
viously mentioned publications for advanced techniques)
At the beginning of a received transmission, the first 0 to 2
bits may be lost while the chip’s receiver settles to the DC
bias point required for the given transmitter/receiver pair
carrier frequency offset. With proper data encoding,
dropped start bits can be tolerated and correct communica-
tion can take place. One simple data encoding scheme is
now discussed.
Generally, a CCT system consists of many transceivers that
normally listen to the line at all times (or during predeter-
mined time windows), waiting for a transmission that directs
one or more of the receivers to operate. If any receiver finds
its address in the transmitted data packet, further action
such as handshaking with the transmitter is initiated. The
receiver might tell the transmitter, via retransmission, that it
received this data, waiting for acknowledgement before act-
ing on the received command. Error detecting and correct-
ing codes may be employed throughout. The transmitter
must have the capability to retransmit after a time if no re-
sponse from the receiver is heard - under the assumption
that the receiver didn’t detect its address because of noise,
or that the response was missed because of noise or a line
collision. (A line collision happens when more than 1 trans-
mitter operates at one time - causing one or more of the
communications to fail). After many re-transmissions the
transmitter might choose to give up. Collision recovery is
achieved by waiting some variable amount of time before re-
transmission, using a random number of bits delay or a de-
lay based on each transmitter’s address, since each trans-
ceiver has a unique address.
An example of a simple transmission data packet is shown
in Figure 32. The 8 bit 50% duty-cycle preamble is long
enough to allow receiver biasing with enough bits left over
to allow the receiver controller to detect the square-wave
that signals the start of a transmission. If there had been no
transmission for some time, the receiver would simply need
to note that a data transition had occurred and begin its
watch for a square-wave. If the receive controller detected
the alternating-polarity data square-wave it would then use
the sync. bit to signal that the address and data were imme-
diately following. The address data would then be loaded,
assuming the fixed format, and tested against its own. If the
address was correct, the receiver would then load and store
the data. If the address was not correct, either the transmis-
sion was not meant for this receiver or noise has fooled the
receiver. In the former case, when the transmission was not
meant for the receiver, the controller should immediately
return to watching the incoming data for its address. If the
later case were true, then the receive controller would con-
tinue to detect edges, tieing itself up by loading false data
and being forced to handshake. The square-wave detection
and address load and check routines should be fast to mini-
mize the time spent in loops after being false-triggered by
noise. If the controller detects an error (a received data bit
that does not conform to the pre-defined encoding format) it
should immediately resume watching the LM1893’s Data
Out for transmissions, the next bit would be shifted in and
the process repeated.
A line-synchronous CCT system passing 3 bits per half-cy-
cle may replace the long 8 bit preamble and sync pulse with
a 2 bit start-of-transmission bias preamble. The receive con-
troller might then assume that preamble always starts after
bit 1 (the first bit after zero-crossing) so that any data tran-
sition at a zero crossing must be the start of the address bits
and is tested as such. The line synchronous receiver oper-
ates with a simpler controller than an asynchronous system.
Discussion has assumed that the controller has always
known when the Data Out is high or low. The controller
must sample at the proper time to check the Data Out state.
Since noise shows itself as pulse width jitter, symmetrically
placed about the no-noise switch-points, optimum Data Out
sampling is done in the center of the received data pulse.
The receive data path has a time delay that, at low data
rates, is dominated by the impulse noise filter integrator and
is nominally
(/2
bit. At a 2 kHz data rate, an additional delay
of approximately
(/10
bit is added because of the cumulative
delay of the remainder of the receiver.Figure 33 shows that
Data Out sampling occurs conveniently at the transmitted
TL/H/6750–35
FIGURE 32. A simple encoded data packet, generated by the transmit controller is shown.
The horizontal axis is time where 1 bit time is 1/(2f
DATA
)
19
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM1893N | RES 250K-OHM 1% 0.125W THICK-FILM SMD-0805 5K/REEL-7IN-PA |
| LM2893M | LM1893/LM2893 Carrier-Current Transceiver |
| LM2893N | LM1893/LM2893 Carrier-Current Transceiver |
| LM2895 | AUDIO POWE RAMPLIFIER |
| LM1895 | AUDIO POWE RAMPLIFIER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1893 WAF | 制造商:Texas Instruments 功能描述: |
| LM1893N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1893/LM2893 Carrier-Current Transceiver |
| LM1893N/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Carrier/Multi-Wire Interface |
| LM1893N/B+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Carrier/Multi-Wire Interface |
| LM1894 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dynamic Noise Reduction System DNR |
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