Read Manchester code from u2270

[viknes1985]

Hi, I tried to get help from many people on machester decoding. No one could help. So i started to read the manchester code. The idea is, if the width of the pulse is 90us, pic start to sample after 45us. So it would always stay in the middle of the pulse. This is so far i got to, but no idea why this never works. anyone, Please help. I'll work on myself on decoding, for now, i just want to read the code from EM4001. If you've any other method, let me know (viknes1985(at)hotmail.com)

[PCM programmer]

Your title says "read from u2270" but your post says EM4001.
Post the actual chip or board you want to read from, and post a link to
the data sheet for it.

[RLScott]

One big problem is that your code does not loop waiting for a rising edge. It checks just once in main(), and then main() exits (probably to Sleep).

Another problem is that you have lots of fputs() function calls. Don't you know that they take time? About 1 mSec per character at 9600 baud. And you are trying to find 90 uSec pulses! You must get rid of all that debugging stuff because it will kill your timing. Find some other way to debug, like writing to spare digital I/O pins. That will only take 1 or 2 instructions.

Another problem is that you seem to want to use Input Capture mode, because you set it up initially. But then you never use it after that. I don't think you understand what Input Capture is.

Once you get the basics out of the way, then you need to study up on the finer points of Manchester coding. Manchester code is self-clocking. That means it contains transitions that you can and should lock to in order to receive it. You apparently are treating 64 bits of manchester as if it were serial Async (as if for a UART). It is not. It has alternating clocks and data transitions. Your code should re-sync to the clock transitions to correct for any slight difference in clock speed between the sender and the receiver. 64 bits is a long time to maintain timing without any re-syncing. Maybe someone else can give a good reference for Manchester - I don't happen to have one handy.
_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting

[viknes1985]

Thanks for the quick replies. This is RFID reader that i'm using www.datasheetsite.com/datasheet/U2270 which read get the codes from EM4001. I need to program the PIC so it could read the manchester code from U2270. Correct me if I'm wrong at anywhere.

If fputc() takes long time, do you have any other suggestion or guide? And how to resync the clock transition of transmitter and receiver?

[RLScott]

[FvM]

[Wayne_]

To add to what has already been said.

#byte b_port = 6
Not needed as you are not using it and you do not specify fast_io for any ports anyway.

#int_ccp1
Directive telling the compiler that the function imediately following is the interrupt service routine for the CCP1 but the function imediately following happens to be main !

SET_TRIS_B(0x81);
Don't need this as again you are NOT using fast_io

Your understanding of manchester code also seems to incorrect.
You should be looking for transitions. A low to high transition in the middle of the bit indicates a 1 and a high to low a 0. You also need to ignore the transition if it is at the beginning of the bit.

You should use these transition not only for retrieving the data but re-syncing your clock or timer.

The hardest part will be trying to determine if the first transition is a data transition (in the middle of the bit) or one you should ignore.

Have fun.

[viknes1985]

Thanks for the reply. Yes FvM, i aware of the bit pattern, according to the datasheet it's 9 bit of 1s. But for now i only wanted to display the the manchester code via hyperlink.

And Wayne, thanks for the advice. I'm still new to this PIC. Still in learning stage, I appreciate your advice. How to collect, let say 64 bits and then store it in a variable?

Thanks.