exxos's Atari, Amiga & retro forum

ijor wrote: 07 Mar 2022 16:10

sporniket wrote: 27 Feb 2022 22:52 And in the mean time, I will have to address that so that "no bit manipulation when load is low" for the next spin.

Might make more sense to do it "only when CS is asserted". This would avoid unnecessarily switching the transceivers on every A5 toggle.

But more important, you should perform a small timing analysis. You probably need faster parts. Why are you using HC parts for the 245's? But putting very fast parts blindly might not be a good idea either. Note that using CS vs LOAD for the control logic would significantly affect the timing. Not necessarily one better than the other in this regard. You have to perform a timing analysis to be sure.

The original text used HC parts, that's why. I used 2 '245 instead of one '243 + one '245 because I manage 7 bits, so I need 14 (2x7), but I admit that I could not figure out how it was done originally.

It would have been great to have figured these things a few months earlier. Oh well. Never mind.

However, I will see what can be done with the current prototype in this thread: https://www.exxosforum.co.uk/forum/viewt ... =29&t=5228

mrbombermillzy wrote: 07 Mar 2022 20:59 I will see what can be done with the current prototype in this thread: https://www.exxosforum.co.uk/forum/viewt ... =29&t=5228

If the prototype gives promising results, I believe that I can find a few easy hardware patches to switch the bits only when /CS is asserted.

sporniket wrote: 08 Mar 2022 04:57 If the prototype gives promising results, I believe that I can find a few easy hardware patches to switch the bits only when /CS is asserted.

Nothing like a few bodge wires on a dev board :) It's part of the course.

Icky wrote: 08 Mar 2022 08:20

sporniket wrote: 08 Mar 2022 04:57 If the prototype gives promising results, I believe that I can find a few easy hardware patches to switch the bits only when /CS is asserted.

Nothing like a few bodge wires on a dev board :) It's part of the course.

Well, I will leave the hardware side to you guys. I don't have much experience with this side of things...especially on the ST. Just let me know what to change and I will get it done.

(The shifter test software will also be the first bit of coding I've done for the ST). EDIT: actually, I made some changes to Gembench for Exxos recently, which I'd forgotten about. Oops! :lol:

So, more enthusiasm than skill in this particular project, but I will try to do my best on the SW side! :)

Just want to thank @sporniket for taking the leap of faith and starting the ball rolling.

After getting encouraging results using the experimental version, it's time to prepare the next iteration. I repurposed the '257 to enable/disable the bit manipulation trick according to /CS. That will ensure that during screen rendering, the databus is transmitted as is to the second shifter.

Small update of the month : with the return of payday, I could order the new PCB, now waiting...

With all the part delivered and some time to do soldering, it's time to build the second prototype.


This time I ordered resistors with color rings instead of digits printed on it, so that I don't have to take care of bending the leads so that the digits are shown. But it's still inconvenient to check...


Anyway let's populate the board...


At this point, I checked the resistors value using a multimeter... And it was the right move : :o :shock: :oops: :cry: :evil:


Damn, I ordered the wrong resistor value. Fortunately, this is easy to fix using 2 7k5 resistors in parallel... 8-)


minus one point for the visual though :lol:


And done, the pink sticker marks the only HCT component I could order, others where out of stock, so I used the spare HC I had ordered last time. It was working so far, so I expect to still be ok.

And not shown is the solder-side generously isolated with polyimide tape.

Time to have lunch :)

edit: reformulation

:dualthumbup:

Looking forwards to seeing if the previous colour errors have been corrected.

mrbombermillzy wrote: 14 Jul 2022 13:19 :dualthumbup:

Looking forwards to seeing if the previous colour errors have been corrected.

So do I :)