Slave PIC to be used like CD4021 chip

[Charles Linquis]

I have done what you describe. The "shifting" was done using SEROUT2 and SERIN2. The "master" PIC sent out 4 bytes of data (in my case) and the "slave" took the bytes
and loaded them into a buffer. The data was followed by a checksum byte. If the checksum matched, the data was written to the port pins. I used a second wire between the two PICs to act as an ACK to indicate a successful trasmission (a pulse LOW was proof that the data got to the slave). The data rate was 19.2 kbaud. Crystals were used on both parts. I used open-collector drive on both lines and 2K pull-ups. The PICs were 6' or so apart.

[skimask]

So, this might be something like an 18F8723, grabbing 64 bits worth of digital data from the various ports and funneling it out the serial port? A 64bit, single chip PISO?

[Charles Linquis]

You apparently are aware of my "chip of choice"!

[skimask]

You apparently are aware of my "chip of choice"!

Started off with the 'broken' 8720, moved up along the way as they've came out.
http://web.ndak.net/jdgrotte/tqfp648...fpadapter.html
Use it a lot, especially when I need to write 'sloppy' code with a lot of debugging type info. I use the extra pins for LEDs, LCDs, switches, etc.
Later on, clean up the code, get it down to size and put it on a 40 pin version of the '8723 (i.e. 18F452/4620/4685, whatever). Have a few of a second version that'll allow the '8723 to plug into a 28-pin socket. Same principle applies.
Very few code changes required as long as I don't use an '8723 specific module or function.

[Darrel Taylor]

Now I read Ioannis' post very different.

I think the idea looks something like this ...



Where the PIC would have a 64-bit shift register, derived from 8 analog inputs, with a serial IN and OUT pin that would make it PART of a long chain of shift registers.

Anywhere close Ioannis?
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[Ioannis]

Hi Boys.

I am sorry Skimask I did not put a schematic or something but was home, late night.

Darrel, that was exaclty the idea and setup! I may say that except you are reading posts very clearly, I think you read minds too!

Charles, your idea is really the oposite of this. And very dependent on the clock. With the circuit that I would post, but Darrel got me, as always he is one step ahead, there is no critical timing needed.

So the PIC would need a 65 bit buffer to store the 64 bits of the analog values and 1 bit for the previous PISO device. This is not limited to one previous of course. PIC does not know what is before it. It just puts on Sout pin the data of its buffer. The buffer fills from the 8 analog and after that, with the Sin data as arrive on each Clock of the relative pin.

It looks like RS232 serial communication but is not RS232. It is just serial 8 bit data transfer without start-stop bits and sychronous relative to the Clock line.

The point for my difficulty is to shift in PBP the 65 bit buffer.

Ioannis

P.S. Sorry for the long post...

[Melanie]

Simply treat the 64/65 bit buffer as a Byte or Word Array... Shift it out using the pointers I've given you here...

http://www.picbasic.co.uk/forum/showthread.php?t=544