Hello,

I have build Ben Eater's circuit of 6502.
I have written a LCD program for 4bit mode and it works. But along with that, I am trying to toggle PORTB, pin0 and it is not working.
Can anyone please look into the code and point out what is wrong?

Thanks

You have print_msg exiting directly to loop, skipping the write to DDRB (and also the write to PORTA). Port B will never switch to an output.

your print_msg loop jumps past the initialiser for the toggle loop, so DDRB is never initialised.

What you could do is change the

reset:

code to initialise BOTH ports, so



Also, what's the clock speed?

Your delay_loop will execute 256 (outer) * 256 (inner) = 65536 times. The inner loop will take 5 clock cycles per loop, so that's 256 * 5 cycles, the outer loop will add another 5 clock cycles per execution of the inner loop, so you're looking at 256 * 5 + 256 * 5 = about 1.6 million clock cycles give or take. At 1Mhz, well that's just over 1.5 seconds, but in the Khz range of the Ben eater thing? A very very long time. Try reducing the ldy and ldx instructions to single digit numbers...

-Gordon

_________________
--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

Thanks very much for your inputs. It works now.
I am wondering how I overlooked this trivial mistake.

And yes, the clock is 1Mhz. I am just experimenting with the delay.
I will switch to the timers for the delay shortly. However, on a side note, the delay is not 1.6 seconds as you have mentioned!.
It blinks as if the delay is around 250 to 500ms! - but that is not the topic for my concern!!!

Thanks for your time guys.

I took a quick stab at it and arrived at ~ 327 ms @ 1 MHz. Now, back to our regularly scheduled program ...

_________________
Got a kilobyte lying fallow in your 65xx's memory map? Sprinkle some VTL02C on it and see how it grows on you!

Mike B. (about me) (learning how to github)

Thanks Mike.
I think your calculations should be correct.

I am actually surprised to see lots of activity in this forum! I thought forums are dead in this age.

I am looking forward to tinker more on the 6502 and custom SBCs!

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

May be the ones I was on are dead (Dead in the sense, users left for some other platforms like reddit or something called discord which I don't even understand how to operate!)

I hope this forum is focusing on 6502 computer - I myself am starting on this topic though (started couple of weeks back to be honest).
I tried to build Ben Eater's 8-bit computer couple of years back (almost 60% complete). But due to the breadboard quality issue, it's still pending. Do you guys have any suggestions on good generic SBC forums where they discuss things like Ben Eater's 8-bit computer?
Since I learnt a lesson due to breadboard quality. This time for 6502, I ordered busboard BB830 ones which did not cause any problem till now.

Thanks.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Thanks very much for your insights, Mr. Garth and Mr. Dinosaur.

I agree that it is frustrating sometimes when Ben glosses over few things in his videos. But nevertheless, I started this hobby after seeing Ben's videos. Thanks for the 6502 primer. I will definitely go through it (given the experience you guys have on this field).

Also on the breadboard part, most frustrating is such parts like the DIP switches which smaller leads popping out randomly!

While watching Ben's videos, I was under the impression that those are the only information I have apart from the datasheets. But now, I see that this site is a gold mine and many experienced engineers both in profession and age

Well I'm intrigues now - obviously my back of an envelope calculations were an order of magnitude out, so let me see if I can get it right.. Just because:

This is the code:



So the inner loop is:



The dex is 2 cycles and the bne is 3 cycles, (but only 2 on the very last one which I never bothered counting before). X in initialised at 255, so the loop count in 255, so that's 254 loops of 5 cycles and one loop of 4 cycles = 1274 cycles.

The outer loop also runs 255 times, so the inner loop will run 255 times 1274 cycles = 324870 cycles.

The outer loop also has an overhead - same as the inner loop which is 254 * 5 + 4 = 1274 cycles.

And that needs to be added (not multiplied which I did before) to the grand total giving 324870 cycles or about 1/3 of a second at 1Mhz.

(plus a tiny overhead for jsr/rts)

Phew!

FWIW: I've used the WAIT routine out of the Apple II monitor in the past for a "calibrated" delay - not really needed here but maybe worthwhile knowing about.

-Gordon

_________________
--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

I'd mention the retrobrewcomputers forum and the VCFederation forums, as well as the Stardot forums, as being active, well-moderated, and adjacent to these interests. You'll get similar advice over on anycpu.org forums, although there are far fewer people there.

I should say you have got a lot of patience. One that I always try to acquire from your generation. And I suppose your username seems to be an anagram of your name? or is it a conincidence?



I went through these. vcfed is something like a collectors forum! stardot and retrobrew looks similar to this site. I feel retrobrewcomputers has some really interesting stuff though! thank you.