Post by thread:Reading Manchester-1 (Bi-phase mark code)

Hi All. I need to read a manchester-1 code signal (also called bi-phase mark code). I was thinking using the CCP module and to detect 1's and 0's measuring T. I'm not sure if this is the best way to do that. I'll appreciate any information or advise. I think that the ideal will be use a single chip for that operation, but I couldn't find any. If anybody know about such a magic IC I'll really appreciate too. Thank in advance Pablo Mochcovsky The Banff Centre for the Arts ____________________________________________________________________ Get free e-mail and a permanent address at http://www.netaddress.com

Pablo;; If the stream is slow enough, you might attempt to decode it real time in the PIC. If not, then the standard operation is to use a PLL to regenerate the clock, and an EOR gate to extract the data from the stream. Then surely you could study the data and clock streams with the PIC. I believe that Burr Brown had some decoders at one time.?? G'luck. Chris Eddy, PE Pioneer Microsystems, Inc. PABLO MOCHOSKY wrote: > Hi All. > > I need to read a manchester-1 code signal (also called bi-phase mark code). I > was thinking using the CCP module and to detect 1's and 0's measuring T. I'm > not sure if this is the best way to do that. I'll appreciate any information or {Quote hidden}> advise. I think that the ideal will be use a single chip for that operation, > but I couldn't find any. If anybody know about such a magic IC I'll really > appreciate too. > > Thank in advance > > Pablo Mochcovsky > The Banff Centre for the Arts > > ____________________________________________________________________ > Get free e-mail and a permanent address at http://www.netaddress.com

On Tue, 31 Mar 1998 13:08:22 -0500 Chris Eddy <spam_OUTceddyTakeThisOuTNB.NET> writes: >Pablo;; >If the stream is slow enough, you might attempt to decode it real time >in the > PIC. You didn't say what speed the signal is. If it is under 30 Kbps or so then PIC software alone would be no problem. At higher rates some sort of external hardware assistance may be needed. Also there is the problem of the PIC being able to rapidly dispose of data that was received at a high rate. Also, its important to consider the quality of the signal. Is the bit rate exactly known, or will it vary? Are the transistions in the signal clean, or are they subject to phase changes and multiple "noisy" rapid transitions where there should be only one? Such factors determine if the decoder can be very simple, or if a more complicated one, optimized for bad signals, is required. A common simple decoder is built around a one-shot timer of 3/4 the bit time. A transition in the signal triggers the timer. Further transitions while the timer is running are ignored. When the timer runs out, the signal level is sampled and used as the recovered data bit. The bit may need to be inverted or xor'd with the last one depending on the exact standard of transmission. If the decoder is in sync, another transistion will occur 1/4 of a bit time later to restart the timer for the next bit. A simple transition detector can be built with an xor gate. One input receives the signal directly. The other one is delayed by a RC network (resistor to the signal, capacitor to ground). When the signal level changes (either low to high or high to low), the inputs to the gate are momentarily different, which causes the output to pulse high. Once the capacitor charges to the new signal level, the output returns low again. These pulses could be captured with a capture timer. A zero bit will appear as a long time, while a one bit will be measured as two short times. The capture timer can also be used without a transition detector, but it's then necessary to reset it for the polarity of the next expected transition. >If not, then the standard operation is to use a PLL to regenerate the >clock, and > an >EOR gate to extract the data from the stream. A PLL-based decoder is good for noisy signals that give simple pulse timers trouble. Often it isn't necessary. Then surely you could >study the > data >and clock streams with the PIC. I believe that Burr Brown had some >decoders at > one >time.?? If you use external hardware to recover the clock and data, a PIC SSP in SPI slave mode would be able to rapidly accept them into the PIC 8 bits at a time. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]