DFBX1 Issues

[charon030]

I figured out that when I remove my NetUSBee in the ROM-Port the board boots up fine with EmuTOS and TOS (MB ROM included or not).

I just don't get how accessing the ROM port is related to enabling the Flash at 50 MHz.

[exxos]

I figured out that when I remove my NetUSBee in the ROM-Port the board boots up fine with EmuTOS and TOS (MB ROM included or not).

I just don't get how accessing the ROM port is related to enabling the Flash at 50 MHz.

There was a huge thread somewhere about NetUSBee and mods done to fix such issues. Maybe someone else can remember the thread..

[stephen_usher]

Stuff on the cartridge port can cause all sorts of bus loading, ringing and other analogue issues.

[exxos]

Stuff on the cartridge port can cause all sorts of bus loading, ringing and other analogue issues.

Indeed, I have battled with that on ST's for years. Inserting a diagnostic cartridge can literally make or break a system, or even changing the ROMs etc. Its part of the reason why the fixes thread exist, but to my knowledge, no one has ever tried changing the pullups on the Falcon to see if it solves such issues or not yet.

[stephen_usher]

Probably better to install a snubber network on the cartridge bus lines. I want to do that on my TT as they ****RING**** like bells, which is probably why peripherals which use the "write using read" hack fail completely. Isolating the cartridge bus behind a set of resistors, as used on the ZX Spectrum, may help as well to dampen things down.

I should design a PCB with a cartridge port edge fingers at one side and a place to fit the edge connector socket on the other with all the lines connected through via resistors and each with a snubber (capacitor + resistor to ground or +5V, doesn't matter). Maybe I can then use the NetUSBee and Spector GCR cartridges. Might be something you can think of @exxos ?

(The Spectrum uses 470R resistors to make a "floating bus", which helps damp reflections.)

[exxos]

@stephen_usher I did use series resistors on one of my early boosters because of bus issues.. It drove me nuts for ages.

The later fix was change the bus pullups. It stiffens up the logic high drive strength (the CPU has like 0.5mA or something very low like that) so the pull ups help being a lower value. Plus it does add a bit of termination which can't hurt.

There are "stair step" pulses which I have seen on some bus lines on the ST.. Where even 2.2K can't solve it.

The Falcon /TT would need a whole new investigation into it all.. And I remember of handle pullups are on the Falcon, but if they are 10K then 4.7K *should* be better ( for future readers , im not suggesting outright do this because it would need a lot of trial and error to see if it makes things better or not first).

Something like a snubber may work, maybe 220R and 47pF kinda thing.. plus additional pullups on whatever lines it uses, maybe 10K.. That may help fix netusbee issues.. but I have enough troubles without starting another investigation :)


You would need a test PCB for the cartridge port where you can scope the source and then add resistors and capacitors and see what the signal results is afterwards.. And of course document the tests in a new thread because it would be useful ;)

[Badwolf]

You would need a test PCB for the cartridge port where you can scope the source and then add resistors and capacitors and see what the signal results is afterwards.. And of course document the tests in a new thread because it would be useful ;)

I, of course, am too lazy to do anything like that. But if anyone does want to undertake such research, I may have a board that could help.

vlcsnap-2025-11-28-14h41m14s261.png

From the as-yet-unfinished Falcon Motherboard Repair part 4 video.

:?


BW

[stephen_usher]

You would need a test PCB for the cartridge port where you can scope the source and then add resistors and capacitors and see what the signal results is afterwards.. And of course document the tests in a new thread because it would be useful ;)

Yeah. I don't s'pose you have a KiCAD footprint for the cartridge port edge connector and socket do you? ;-)

[exxos]

Yeah. I don't s'pose you have a KiCAD footprint for the cartridge port edge connector and socket do you? ;-)

Nope, but I believe @sporniket STE recreation is public somewhere with all the lib for KiCAD.

I gave up with KiCAD when they screwed over win7 users :roll:

[Badwolf]

You would need a test PCB for the cartridge port where you can scope the source and then add resistors and capacitors and see what the signal results is afterwards.. And of course document the tests in a new thread because it would be useful ;)

Yeah. I don't s'pose you have a KiCAD footprint for the cartridge port edge connector and socket do you? ;-)

Here's the cart lib I made.

I think the socket is a standard edge connector one, just rotated 90 degrees. If you can forgo the rotation it should be straightforward.

BW