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Topic: What chip is can I use on v3? (Read 4801 times) previous topic - next topic

What chip is can I use on v3?

Hello,
Question is, where can I find chip used in v3 hardware layout. On schemaic there is PIC18FJ2x50 in TSSOP. I did not find any pic with that number. There is PIC18F2550 like in older layouts but on manufacturer site there isn't TSSOP package. What chips fits to this prject and where can I find them?

Re: What chip is can I use on v3?

Reply #2 –
Thank you mikelelere - I was not familiar with PIC18F family on level that I could replace x.

Re: What chip is can I use on v3?

Reply #3 –
Any of these are better though as the 24J50 may not have enough memory for the full firmware.

18F25J50
18F26J50
18F26J53
18F27J53

In any case  you will have to modify the firmware and that is not easy if you do not understand USB and maybe the PPS as well.

Re: What chip is can I use on v3?

Reply #4 –
Well, yes. While it might be possible fitting the full firmware in 16KB, using one of the MCUs suggested by Simpkins might be a safe bet. Anyway, this is the program memory usage reported by the C18 compiler for the 18F2550 (and AFAIK, the only available firmware version for now. You'll need to modify the existing firmware or wait for somebody else to do it):

                              Program Memory Usage
                              Start        End     
                          ---------  ---------     
                            0x000000    0x000005     
                            0x000008    0x00000d     
                            0x000018    0x00001d     
                            0x000800    0x000805     
                            0x000808    0x00080d     
                            0x000818    0x00081d     
                            0x00082a    0x003af5     
                            0x300000    0x300003     
                            0x300005    0x300006     
                            0x300008    0x30000d     
            13052 out of 33048 program addresses used, program memory utilization is 39%

Re: What chip is can I use on v3?

Reply #5 –
Glad you edited. I was getting ready for a fight. :)

13052 out of 33048 program addresses used, program memory utilization is 39%  + 2KB worth of bootloader.

The firmware hex file I have here, which I believe is the official supplied V22 firmware, is 15.9K long (based on the last used rom address) already so you would want to be betting on any new firmware getting smaller, not larger.

Then there is the problem that the last page of the j-series cannot be used "in practice" because the config words are stored there and cannot be "safely" erased by the bootloader. That is a whole 1KB gone.

You could rearrange the code so the bootloader is loaded high and save (gain) 1KB but it is really getting much harder.

For a few penny more the 18F25J50 is looking gooder. :)

Re: What chip is can I use on v3?

Reply #6 –
First of all peace... :-)  I prefer discussing to fighting!

Second, yes it is better using 18f25j50 to stay safe. I edited because I did not want our friend cooler1989 to spend money on a part that could not be (easily) used for this project. However, I still belive it is possible (not sure whether the bl would also fit or not, but I never made such claim). Moreover, I recall that most firmware images provided here are compiled with a limited (not optimizing) evaluation version of C18 that produces larger binaries than those produced by the licensed version. I know it because I have compiled myself other different firmwares from projects belonging to this site with the licensed version and the differences in size are quite noticeable.

Still, I  agree that using a 18f25j50 instead of a 18f24j50 is a safe bet since (I believe) both the 2550 and the 25j50 have 32KB of program memory. Either using 24j50 or 25j50 would obviously require modifying the existing code. It shouldn't be too hard though. If you check the schematic,there are only minor hardware changes: instead of being connected to  more than one pin of the MCU that provide different functionalities, now the IRRX, IRDETECT and IRTX lines are connected to remappable pins that provide all the required functionalities via PPS: PWM for generating the IR carrier, Capture module, EXT1 and  interrupt on change facilities for measuring infrared pulses and to measure carrier frequencies. Regarding the USB code, provided that you use the DP USB stack you will have to make little changes (if any at all) to the existing code. Minor changes will be also required when configuring the timers and the capture/PWM modules.

Hope this helps.