A strange PIC problem

Jan Panteltje · 2010-03-11T22:40:54+00:00

I was writing a driver for a graphics LCD for PIC 18F14K22.That went OK: ftp://But I wrote it is asm, so it needed a lot of typing,even more so because this display CD-19-HG1286418C has a strangedriver chip S6B0108 that comes from a planet where x is vertical and yhorizontal,and people write from to top to bottom probably on the right side towards theleft...and the display uses 2 driver chips for each half... so it took a lot of keyhitting: ftp://to get it to do things the European way, that I then reversed with x0, y0 atbottom left asthat is easier for what I want to do.But now about the problem.I did all this with the 8 MHz PIC internal clock, and it works perfectly.Activated the internal 4 x PLL, so to 64 MHz internal clock, results in 16MHzprocessor clock.Display stopped working, only display on and display off command still worked,.Well, added the usual delay between I/O operations, but this time,even with seconds delay, no effect.Finally grabbed the scope, and looked at the PIC pins.Now this is strange: bsf PORTA,1 ; pin 18 LCD_C_D bcf PORTA,5 ; pin 2 LCD_WRshould set pin 18, and then clear pin 2This is what happens at 16 MHz clock.But at 64 MHz clock after the first instruction pin 18 does not go high, |||||||||||||||||||||||||||||||||||||| porta, 1_________||||||||||||||||||||||||||||||||||||||_____________________ pin18 16 MHz RF----------------------------------------------- | porta, 5 |_________________________ pin 2 ^ ^ | | bsf PORTA,1 bcf PORTA,5 but start outputting 16 MHz until the second instruction, and then goes to_zero_,the second instruction operates normally and clears pin 2.It seems the PIC internal...

Mar 11, 2010 25 Replies

Rate this thread:

Jan Panteltje 16 years ago

On a sunny day (Thu, 18 Mar 2010 12:57:15 +0000) it happened Nobody wrote in :

The situation in other circles may have been different. The other

Sinclair Z80, ZX81, and Spectrum were Z80 basesd and had not that bug :- Z80 has no bugs as far as I know, and I coded a lot for it. It has many 'hidden' instructions though. Wrote a disassembler for it:

formatting link

I never used the 6502 myself.

Vote

John Fields 16 years ago

Pity... It was basically a 6800 with no hardware multiply. JF

Vote

Fred Bartoli 16 years ago

John Fields a écrit :

IIRC the 6800 didn't have any hardware multiply. It was the 6809.

Thanks, Fred.

Vote

Michael A. Terrell 16 years ago

formatting link

Sigh. Commodore published technical manuals for the VIC-20, C-64 and most other computers they sold. They had schematics and data sheets on the 6500 series ICs. Other companies published a lot of books after reverse engineering the commodore line. i still have most of mine, including the ones about the 1541 and other drives.

Lead free solder is Belgium's version of 'Hold my beer and watch this!'

Vote

Joel Koltner 16 years ago

Yep, and simple-minded assemblers/disassemblers like Supermon by Jim Butterfield were available pretty much immediately upon their release -- since I believe he already had them for the PETs and just needed a few quick code changes to work on the VIC and C-64.

I think I first heard of this particular problem in some article on software copy protection that suggested that making use of this undocumented behavior of the 6502 might lead would-be pirates astray. In retrospect I doubt that would stop anyone for very long -- if you knew anything about hardware design it might occur to you that something "funny" might be happening when you crossed a page boundary. (Granted, no Google back then to verify/communicate such ideas almost instantaneously...)

"Mapping the C-64" and "Inside Commodore DOS" were awesome... those and the Commodore hardware reference manual were a very good starting library.

---Joel

Vote

Jamie 16 years ago

Stop it, you guys are reminding me of my age!!!!!!!!!!!!!!!

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required