PIC16F877 to PIC18F4550 code migration

[beaker404]

Any gotchas on this topic? I have code that runs fine on 16F877, moving to 18F4550 for more ram for improvements. I have stripped the code down to looping and sending a serial stream to hyperterminal. Scope shows waveform for sending, hyperterminal displays nothing. PCB works with '877 programmed with old code, so I think the hardware is ok. changed the crystal from 4MHZ to 20MHZ and 15pf caps for the '4550. I am set for 9600 8 N 1.
Code snippet of start of code:
main loop consists of a continuous while loop using fprintf. No interrupts are being enabled at this time, stripped all that out.

[Ttelmah]

Are you intending to use USB?. The fact your are calling the serial 'USB_SERIAL', suggests this. If so, the clock needs a lot more setting up:

[beaker404]

Not using the USB ports on the chip. Poor naming on my part, there is an adapter that goes from TTL to USB on the board. This all works with '877 code. I suspect it is something to do with the 18F chip setup but I have been unable to find anything on the topic. I am using C6 and C7 for serial as the USE statement states.

[beaker404]

One additional observation, my timing may be off from the crystal, a .5 sec delay seems to be allot longer when observed. Does the CPUDIV still need to be set up? does it influence the hardware UART on pins C6 and C7?

[beaker404]

UPDATE, figured this one out, needed the CPUDIV1 callout in the #FUSE. That got my timing right and the serial started working again. You were right, default was CPUDIV4 causing my clock to be slow and serial to be way off.

[temtronic]

glad to see you got it 'up and running' ! I remember the 'fun' using it, ended up printing the 'possibe clock data paths' diagram and HIGHLIGHTING exactly what I needed. THAT helped me see what bits in which registers had to be set.
One of those 'picture worth 1000 words' moments !!

Jay

[gjs_rsdi]

Migrating from 16F877 to 18F4520 is strait forward, pin to pin replacement, done it in the past.
If you are not using USB, why the 18F4550?

Best wishes
Joe

[Ttelmah]

As I said the default for the CPUDIV is /4...

Have to agree wholeheartedly with gjs_rsdi's comment.

Unless you intend to switch to using the PIC USB in the future, using the 4550, costs you three I/O pins & extra power (the USB PLL permanently runs).

Pointless. There are much easier 'straight swap' chips, and some the offer
extra features (like an extra serial etc..).

The 4550, is a poor choice as an straight upgrade to the 877.

For a modern chip, the 18F45K22, has extra serials, more RAM, more ROM, etc. etc.. It is also half the money!...

The 4520, is also more money now than the more modern chip, though is otherwise a good alternative.

[temtronic]

Like others, I did the 877 to 4550 thing, when I found out the USB drivers used up 1/3 code space, re thought the PIC choice. I'm now using the 18F46K22 for 99% of projects. Yes, overkill for 99% of them, but 2 HW UARTS, lots of mem and I/O pins! For USB I use a $2 TTL<>USB module.
When you consider PIC4550<>USB, you need to price out connector, caps, resistors, pcb space, etc. That will chew up a good part of $2 ! Then there's the driver space and PCb layout (D+, D- <> D-,D+ !) That $2 module frees up code space, has a couple LEDs, properly connected AND it works !
While there may be a 'better' PIC today, unless you're ordering 10,000 pieces, the additional cost per PIC isn't great compared to R&D costs ( seldom considered) or TIME wasted on 'internal USB issues'.

Jay

[asmboy]

i want to strongly second jay- 18F46K22 is your friend and so easily back compatible to 4620, 4525 etc etc.

my most recent design was K22 but built with 4525 in production. Just avoid the higher numbered timers for back compatibility.....
(only used the 4525 because we had hundreds unused in old stock .)

4550 is antique history IMHO

[Ttelmah]

Just to triple the comment, the 45K22 I mentioned, is the same chip but only half the ROM. I should have said 45K22/46K22.

[gjs_rsdi]

As all the veterans have stated, 18F26K22 & 18F46K22 is the way to go.
Still for someone who works with 16F877 will be much easier to move to 18F4520 or 18F45K20 and then to learn how to work with 18F46K22.
I had not small difficulties to migrate from 18F25K20 to 18F26K22

Best wishes
Joe

[dan king]

not to hijack the thread but ....

is anyone aware of a good breakout board with the 46k22 mounted? I have been using the 18f2553 because the Sparkfun breakout board with USB is so convenient. I would consider the 46k22 using an ftdi if a nice breakout was available.

Thanks

Dan

[asmboy]

nice inexpensive module

http://www.futurlec.com/PIC18F46K22_Controller.shtml

plus

http://www.ftdichip.com/Support/Documents/DataSheets/Modules/DS_UM232R.pdf

[dan king]

thanks for the links, I'll check it out.

Dan