Subject:
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Re: what is NRZ ???
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 22 Mar 1999 13:02:10 GMT
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Original-From:
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dave madden <dhm@webvision.comANTISPAM>
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Viewed:
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1071 times
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"Erling :O)" writes:
=> when you write:
=> The IR protocol associated with sending a "message" to the RCX is=20
=> prettysimple. Bit encoding is 2400 baud, NRZ, 1 start, 8 data, odd =
=> parity, 1
=> stop bit. A '0' is coded as a 417us pulse of 38kHz IR, a '1' bit is =
=> 417usof=20
=> nothing.
=>
=> what dose NRZ mean ?
A search for "NRZ encoding" at Alta Vista returns this:
NRZ Encoding is a two-level, non-return-to-zero signaling
mechanism used to transmit data and link status control signals
onto the network medium.
Using NRZ encoding, one bit of data is transmitted per clock
cycle. A bit value of 1 is detected when a high voltage signal is
transmitted, and a bit value of 0 is detected when a low voltage
signal is transmitted.
So, paraphrased (if I recall my EE correctly, and I probably don't)
it's the most obvious way of sending information serially: use a high
voltage (or in this case "417uS of nothing") when you mean "1", and a
low voltage (or "a 417uS pulse of 38kHz IR") when you mean "0".
This is in contrast to other signaling schemes one could use that have
properties (other than simplicity) that are needed for a particular
application. For example, there's an encoding scheme (maybe NRZI -- I
couldn't find a simple description on the Web) where a "0" is encoded
by a single high-to-low or low-to-high transition, and a "1" is
encoded by two transitions (low-high-low or high-low-high). This has
the advantage that even if you send a bunch of 0's or 1's in a row,
there are still transitions occurring in the raw input stream that you
can use to keep your clock in sync.
As far as it applies to the RCX, unless you're building an IR tower
from scratch or programming some device to act like a tower, you
don't care whether it's NRZ.
d.
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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