PIC to PIC communication (suggestions)

The current project I am working on right now will be to maximize I/O pins without going completely serial (serial communication, not YouTube - Al Gore Im Serial!). I am using a 18F4620 connected to a 18F2525. The way in which I have parts connected, is that It requires 6 I/O pins to run the SN754410 Dual H bridge. I will be using the 18F4620 to output a binary value using 3 I/O pins, in which I will OR together with the 18F2525 and drive high the proper pins afterward. You may say it will be easier to just drive the 18F4620 with 6 I/O pins in the first place, but I am looking at the total of the 4620's pins, not about the 2525's, in a sense the 2525 is a demultiplexer.
Truth table of 4620 & 2525
0 0 0 Null
0 0 1 Forward Motor A
0 1 0 Forward Motor B
0 1 1 Backward Motor A
1 0 0 Backward Motor B
1 0 1 Forward A + B
1 1 0 Backward A + B
1 1 1 High Brake

The three inputs on the left will be the 4620, and the name is the appropriate motor that it will be driving. Otherwise, the 2525 will take the inputs and turn on the appropriate ports to replicate the results on the right. I have already implemented both systems, but I have yet to merge them together to create a demultiplexer, but I can.

Really what I am asking is for your past experiences and tips of PIC to PIC communication and any suggestions that you have.

The communication you have outlined is a 3 bit parallel system with no hand shaking. A strange choice if you goal is to save pins.

Serial from the UART could be done with 1 pin. Or you could go I2C or SPI.

3v0

Krumlink said:

Really what I am asking is for your past experiences and tips of PIC to PIC communication and any suggestions that you have.

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The easiest way is to go 'completely serial', you can use the USART's which would take two pins (one each way), or if you do it in software you can use just a single pin and a little 'clever' programming.

while were on the topic, how does serial pic to pic communication work? anyone have a good website about it?

While at school today in my free time I devised a new communication system with handshaking and status. It will be a 6 bit parallel communication that will have the ability to read and write to the other device, and a status that would indicate whether or not the PIC was receiving data. 6 bit allows for up to 64 states and would only require a single port. I will be testing the transmission protocol between 2 18F1320's.

Triode said:

while were on the topic, how does serial pic to pic communication work? anyone have a good website about it?

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There are several methods of communicating data between PICs, and the way that I thought of this was to decide between parallel and serial. I chose parallel and then I needed to figure how many states I wanted to have.

Still a confusing choice when you already have what you need with 2 pin RX and TX UART. Is there a reason your using a parallel scheme, or is it just an experiment?

DirtyLude said:

Still a confusing choice when you already have what you need with 2 pin RX and TX UART. Is there a reason your using a parallel scheme, or is it just an experiment?

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Both an experiment, and the TX&RX pins on one PIC is already being dedicated to PIC to PC communication.

The C18 lib has bit bang code for a software UART. You can place it on any pin. It will still be fast enough. Only 2 pins.

3v0 said:

The C18 lib has bit bang code for a software UART. You can place it on any pin. It will still be fast enough. Only 2 pins.

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Yes, serial is the way to go, a six wire parallel interface is sheer folly.

It could be that krumlink want to play with a parallel interface.

3v0 said:

It could be that krumlink want to play with a parallel interface.

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Maybe, but why use a 6 bit one?

Could be he has six pins left or he only needs 6 bit command words.

Could also be 6 bit data and the 2 handshake lines, using a full PORT.

Parallel transfer can be much faster than serial, if time is an issue.
From what he says, he is not transferring ASCII text, but 64 command/control states.

Oh my. I need one of those emoticons that shows the little smiley face guy eating popcorn.

Like that?

The port sounds good. Go for it.

shingadaddy said:

Oh my. I need one of those emoticons that shows the little smiley face guy eating popcorn.

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Can you say what this has to do with this topic.?

Yes. Perfect mister_e!
As for the topic, everything and nothing at the same time. It seems to have made its way off in the weeds.

"The current project I am working on right now will be to maximize I/O pins without going completely serial"

"the TX&RX pins on one PIC is already being dedicated to PIC to PC communication"

Krumlink appears to be intent on going PARALLEL- ONLY!. "Sheer folly" Nigel suggested serial anyway (great idea to save pins!) and then shot out the raspberry as in "HUMOR". And of course Triod dropped the thread hijacking SERIAL subject in the mix. Yep parallel is gonna be faster of course.
Parallel-serial-parallel-serial-3bit-6bit-8-bit

I just saw it going oscillatory divergent and added a little damping. (Humor). Have I upset the humor police on the board?

Triode said:

while were on the topic, how does serial pic to pic communication work? anyone have a good website about it?

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see:

**broken link removed**

but:

I think spi or i2c serial is probably the way to go, they are serial methods for microcontrollers.