PIC...

L

Lliam20789

New Member
Not sure if you guys want to hear about this, but i'd like to experiment with a PIC chip...

Any one know somewhere that will send decent (quality) samples shipped to Australia? I've had a look but the one's I've found only do this for universities etc...

Thanks.
 
J

jodicalhon

New Member
If getting free samples is a problem, a PIC 16F628A is reasonably cheap from Altronics. ($8.50).

This is an 18 pin device, with 2k (word) Flash, 228 bytes of SRAM, and 128 bytes of EEPROM. I had some fun flashing LED's with it a while ago, but my experiments have stalled lately as I can barely find time to play with my Picaxes at the moment. :(
 
hippy

hippy

Technical Support
Staff member
There's no reason you shouldn't just erase a PICAXE. You can start with an 08 see how it goes.

I did an assessment of 'most capable' PICmicro in terms of best all-round platform to write any software on. It doesn't help choose the best PICmicro for any particular project but this has been very handy when having to decide which to buy or the best samples to get.

My assessment was based on a reference of DIP packaging, 4K Flash, 256 Data Eeprom, 256 User SFR ( Ram ) and having Internal Oscillator. Score on far right indicates its usefulness, the higher the better. See attached. There may be other, better PICmicro's since that list was created.

My conclusions for what to get were ...

For 14-pin use ... 16F688
For 18-pin use ... 16F88 (18X), 18F1320, 30F3012
For 28-pin use ... 16F886 (28X1), 18F2550
For 40-pin use ... 16F887 (40X1), 18F4550

The dsPic30F3012 is the only one I'm aware of in DIP form, has a different instruction set to 16F/18F, needs a completely different suite of software to normal Microchip MPASM and most 16F programmers do not support it, so probably for more experienced users only.

Four personal recommendations -

1) It's soon to be Christmas; any 'samples' Santa brings are de-facto free :)

2) Get three of any selected chip and expect at least one to involuntarily expire

3) Don't casually reject the 18F's

4) Buy the Microchip Pickit2 programmer
 

Attachments

Last edited:
T

Tom2000

Senior Member
I second your pick of the 18F1320. Great part.

Although I've been using 18F2431s for my 28 pin work, the 18F2550 is impressive. I've got one on hand, but haven't played with it yet.

I recently received a 30F4013. It's a 5 volt part in a 40 pin DIP. Still wading through the documentation and tools for the dsPIC line. There's a real learning curve there, one I didn't expect to encounter.

For 8 pin chips, I don't think anything beats a 12F683. They did a very nice job with that chip.

Tom
 
hippy

hippy

Technical Support
Staff member
Thanks for the pointer to the 30F4013. I'll have to go and check what else I've missed since creating that list. I haven't done anything with the 30F because it really is not for the faint-heated. I'd hoped it would simply be a case of changing the 'device' header, use the correct syntax and run MPASM, but no way is it that simple.

I didn't count the 12F683 etc because I focused on those which can do self-programming and could have a serial bootloader built into them. There are so many different PICmicro variants that it can be hard to choose any particular one even when you have a final application in mind !
 
T

Tom2000

Senior Member
hippy said:
...I haven't done anything with the 30F because it really is not for the faint-heated...
Click to expand...
"Truer words were never spake!" :)

You're so right, hippy. I thought that transitioning to the dsPIC family would take me about one weekend of concentrated study. After all, it's a PIC, isn't it, and I'm comfortable with PICs.

WRONG!

It might resemble a PIC, but working with dsPICs is a totally different experience, in a totally different environment. Or so it seems to me at my novitiate stage of the learning process.

If I have even the simplest DSP app running on it by Christmas, I'll be patting myself on the back! And if I don't, I won't be at all surprised.

Tom

PS - I forgot to second your Pickit2 recommendation. I've got one, and it works well. It can't be beat for USD$35.
 
Last edited:
hippy

hippy

Technical Support
Staff member
Wow - A lot more DIP packaged 30F's and other high-end PICmicro's than when I last looked. This is where I think the future should be for PICAXE-X3's.

Some very nice things about the 30F range, particularly top speeds of 120MHz (30MIPS) even from the internal oscillator. That's 15 times faster than an 8MHz 18X and 7 times faster than a 16MHz 28X1. At those speeds, PICAXE Basic wouldn't be much slower than PICmicro Assembler at 4MHz !
 
L

Lliam20789

New Member
Thanks for all the great input!

At the moment I'm thinking Hippy's suggestion of the 40 pin chip would be good. I could make a simple onboard download circuit and breadboard arrangement... be good to experiment with... does anyone know where to find good circuit schematics etc?

Lliam
 
T

Tom2000

Senior Member
By the way...

hippy has mentioned, a time or two, Picaxe peripherals built using other processors.

About a week ago, I started designing one, too: a 24 character x 13 line alphanumeric display for your oscilloscope, using a PIC 18F1320. It didn't take me long, though to realize that such a device has absolutely no purpose.

While I was thinking about the project, though, I started thinking about names for such Picaxe peripherals. In the Arduino world, they call their add-on boards "shields."

I propose that Picaxe peripherals be called "Shovels." :)

Tom
 
hippy

hippy

Technical Support
Staff member
Lliam0002 said:
I could make a simple onboard download circuit and breadboard arrangement... be good to experiment with... does anyone know where to find good circuit schematics etc?
Click to expand...
The PICAXE circuits are as good as any. If you are thinking of creating PICmicro firmware which includes a serial bootloader or needs to talk to or from a PC you may as well use the same pins as the PICAXE does. Your PICmicro can then drop into any PICAXE board and you can use the download cable you already have for comms.

If you're using a programmer like Microchip's Pickit2 that uses ICSP; you can either put ICSP on the target board or you can build a separate board just for programming. The second is easiest but Microchip have an Application Note on how to design circuits for ICSP and there are plenty of examples found via Google.

If you program in a serial bootloader, you only usually need to program it once, after that you can use it in a PICAXE board exactly how you'd use a PICAXE, albeit with different download software.
 
L

Lliam20789

New Member
Good suggestion Hippy, Thanks!

So a PICAXE 40X1 wiped in a PICAXE board will be able to be programmed through the same download port as the original PICAXE?
 
hippy

hippy

Technical Support
Staff member
Unfortunately the PICmicro internal UART isn't ( usually ) on the download pins a PICAXE uses and the polarity of the signal is inverted so cannot be used with the simple two resistor interface as used by the PICAXE.

To use the two resistor interface means having to write bit-banged serial code. It's not that hard but it can be a challenge getting the baud rate timing spot-on and the entire downloader down to just 256 instructions to allow the code to be write protected.
 
J

jmumby

Senior Member
Like the second post says microchip. I have got samples easily and I'm in NZ and nobody wants to send anything there for free!
 
D

demonicpicaxeguy

Senior Member
hippy said:
Unfortunately the PICmicro internal UART isn't ( usually ) on the download pins a PICAXE uses and the polarity of the signal is inverted so cannot be used with the simple two resistor interface as used by the PICAXE.

To use the two resistor interface means having to write bit-banged serial code. It's not that hard but it can be a challenge getting the baud rate timing spot-on and the entire downloader down to just 256 instructions to allow the code to be write protected.
Click to expand...
why not just invert everything you send and recieve.....?
 
A

andrew_qld

Senior Member
hippy said:
Unfortunately the PICmicro internal UART isn't ( usually ) on the download pins a PICAXE uses and the polarity of the signal is inverted
Click to expand...
The serial in/out pins were the same on the 16F877A as the 40X, but yes you do need a MAX232 or similar inverter.
 
hippy

hippy

Technical Support
Staff member
Are you sure about the pinout ? The PICAXE datasheet shows legs 6 and 7 used for download, the UART for the 877A is on legs 25 and 26.
 
A

andrew_qld

Senior Member
Oops!
You are correct of course Hippy. I wrote that post at the end of a very long day. My appologies.

When I had quick look at the picaxe datasheet I confused the hardware "hserin/out" ports with the programming ports. I should have realized, I've built a few boards with the 40X / 40X1.

The problem with is that unlike the Picaxe, you can't leave the hardware USART hooked up to equipment and still download a program. Then again you can go to 115200bps on that port (they are apparently working on a bootloader this speed).

Cheers,
Andrew
 
Last edited:
You must log in or register to reply here.
Top