Originally Posted by GatorGuy

I would like to connect the main PIC to the other PIC's I/O pins to either send data/commands or to retrieve data such as temps.

And what protocol are you intended to use for all these two way communications that happen between the chips, in real time? If you have no clue, forget the whole idea of connecting several PICs together.

What's wrong with just one PIC with lots of I/O pins like the 16F877, unless two way communication is the real objective of your project.

It's easy enough to do, just a simple serial interface between the PIC's is all you need, you just have to decide on a protocol to use!. This obviously depends entirely on how it's all required to work together.

There was a website with a project called 'PICNet' which used serial connections, and 'PICNet USB' which used the 16C745's USB port, and 'networked' a number of PIC's together. Unfortunately the site seems to have disappeared?.

There's I2C on many PICs too. That manages it automatically so there will be no conflict between multiple transmitters, the protocol already handles addressing and in any case is an open-collector scheme that rules out electrical conflicts between transmitters.

Downside is it's not made for long runs (though it can sometimes be rigged to do so). You can find many non-PIC devices like ADCs, etc that work with I2C. The PIC implementation is a bit dicey too, it's not well documented and there are some known errata issues on a lot of parts.

Originally Posted by supremo

Hi, sorry to hikack the thread...

I had prepared a thread which is very similar so I decided to just ride on this thread instead.

When I realized I needed mre I/O pins, I was thinking along the
serial connection of 16F628s. My only reason for not going to
the higher pinned PICs is because I'm a newbie to PICs and is relying
on the tutorials available in the web.

Now, if there a direct conversion if I developed a program starting
with the PIC16F84A and then converting it to PIC16F877?

For a start you shouldn't really use the 16F84!, it was replaced years ago by the higher spec and cheaper 16F628.

However, BOTH are almost completely compatible with the 16F877, all of them use EXACTLY the same 14 bit core. The only differences are due to the hardware extras on the different devices.

I suggest you have a look at my tutorials, which use the 16F628 and 16F876/7 - I also give details of the very slight changes required between the two processors.

Originally Posted by Pommie

Contra to what most people state, the 16F628 is not a good replacement for the 16F84. The 16F628 cannot run unmodified 84 code yet there are many pics that can. The 16F877 can run unmodified 84 code. Just pretend it's a 84 with lots of I/O ports.

Mike.

I think 628 is a better replacement for 84 than 877. Try ti fit 16F877 in the same socket as 84 :lol: , And to add to lines of code into 628 is not a big deal!

Originally Posted by Pommie

Contra to what most people state, the 16F628 is not a good replacement for the 16F84. The 16F628 cannot run unmodified 84 code yet there are many pics that can. The 16F877 can run unmodified 84 code. Just pretend it's a 84 with lots of I/O ports.

Sorry? - the 16F628 is the official MicroChip replacement for the 16F84, and has been for many years - it's uses EXACTLY the same 14 bit core, and there's even a migration document which tells you exctly what slight differences there is!.

The only 'modification' required to the code is to add two lines that disable the comparators - this is extremely trivial to do, and well documented. The 16F877/6 requires MORE changes to 84 code to allow it to run, at least four lines to turn the analogue inputs off (as it requires bank switching).

So contrary to what you appear to believe?, the 628 is the perfect replacement for the 84 - as it was designed to be!, and certainly closer than the 877.

If you want a version with analogue inputs?, try the 16F819 and 16F88, these are 18 pin but have analogue inputs. As with the rest they use the same 14 bit core, and are trivial to use in place of a 16x84.

Originally Posted by Nigel Goodwin

Originally Posted by Pommie

Contra to what most people state, the 16F628 is not a good replacement for the 16F84. The 16F628 cannot run unmodified 84 code yet there are many pics that can. The 16F877 can run unmodified 84 code. Just pretend it's a 84 with lots of I/O ports.

Sorry? - the 16F628 is the official MicroChip replacement for the 16F84, and has been for many years - it's uses EXACTLY the same 14 bit core, and there's even a migration document which tells you exctly what slight differences there is!.

The only 'modification' required to the code is to add two lines that disable the comparators - this is extremely trivial to do, and well documented. The 16F877/6 requires MORE changes to 84 code to allow it to run, at least four lines to turn the analogue inputs off (as it requires bank switching).

So contrary to what you appear to believe?, the 628 is the perfect replacement for the 84 - as it was designed to be!, and certainly closer than the 877.

If you want a version with analogue inputs?, try the 16F819 and 16F88, these are 18 pin but have analogue inputs. As with the rest they use the same 14 bit core, and are trivial to use in place of a 16x84.

Pommie: Exactly as I said :lol:

Originally Posted by Pommie

Well, that will teach me to come in from the pub and start spouting.

While I didn't explain myself as well as I would have liked (call that wrong) I do feel that I have a point though. The 628 has these comparators that nobody uses. Had they not put the comparators in there then it would have run 84 code without any changes (recompiled with the inc files). AND, if the person that asked about the 877 used the additional ports instead of that inferior A port then it would run 84 code unchanged (I know, I'm reaching). Anyway, the person that asked about the 877 can be assured it will work.

Next time I'll wait till the morning.

Mike.

You have partial truth, but we were talkiing about Drop-in replacements, which 16F877 obviously isn't...

BTW: Good Night :wink: