Fix your OCM

Finally. Don't need to use a slot-expander any more

@gdx, why not?

@robotsoft. If you had an error, can't find the nowind it is possible.. but there are more failures possible of course

If that electrical tape gets loose inside the cartridge slot... Let's say it's not good. I don't think it's a good idea to suggest that course of action.

I see the post could be .. place non conducting tape over pin 10 .

How does the moonsound not work in unmodified state?

Edit: I thought I had it working in the past, but checking the video it was ocm with dalsori 1. It plays, be it very unstable in tempo.

The unfixed sentence can still be read a few lines up. Method 3 is also mentioned with 'the fix'.

You mean also when used on a 'regular' MSX?

I see strange behavior when combining my slotexpander with GR8NET in the other primary slot. Combined with f.e. the MFR it works fine, so until now i suspected the GR8NET. Can this be the same problem?

Is that really an issue with the devices? If I'm not mistaken busdir should be Z (high impedance) or gnd, so having them all connected wouldn't be a problem, isn't that a problem on the cartridges not putting the output at high impedance when not asserting busdir?

Is this to solve the same problem as mentioned here: Hardware issues on Zemmix and others

could someone post a photo of this fix?

Hi everyone. Don't get confused. This fix is ​​not necessary if there are no problems with the cartridges or if you are using a single slot at a time. It also does not affect the previously published fix, this is a new fix.

If the cartridge works fine on its own and only stalls when combined with other cartridges, this patch will fix the problem. Therefore I recommend that you try method 3 temporarily and apply method 1 when you are sure that method 3 worked.

msd: the busdir signal has nothing to do with bus mastering. It's intended for those MSXs that have a buffered databus on the cartridge slots. i.e. through a 74LS245. That is a bidirectional transceiver, and one pin controls which direction the signals can go. Normally it goes toward the MSX (for reading ROMs etc), but if you want to write a byte to a cartridge (I/O port) the direction has to be reversed. This is why it's implementation is required on MSX cartridges that need to be written to (sound cartridges, memory mappers etc). Buffered databus is not required in the MSX standard, on those MSXs that don't have the buffers the BUSDIR signal is simply not connected.
So:
- Cartridges that implement I/O must implement BUSDIR
- MSX hosts implementation of bus buffers and BUSDIR is optional

Yeah, problem is that I/O addresses do not relate to a slot, so there is no slot select and there is no way to each buffer know if the IO read will be from it or another slot sharing the same bi directional buffer.

But MSD question still is valid, on a system that busdir is not needed, it should not be an issue to have a collision of signals that are not being read by anyone, my SM-X has an OPL4 and a 9990 from tecnobytes and I use both at the same time to play life on earth. My guess is that for some chips the power drained during the collision is causing erratic behavior, and perhaps of the design buffered busdir there is less chance of such collisions causing an issue

Correct" slot expanders always contain a buffer a" .. That is why a slotexpander can fix some issues.. For example a novaxis scsi interface only work with a slot expander in a nms 8245.

I also cut my DEOCM.

https://twitter.com/thara1129/status/1296812918290300929

Seems one chip msx also has busdir of each slot connected to the same fpga pin, so, short circuiting busdir of both slots

You’re thinking of another problem.

It can be done in various ways. But the problem remains upstream, as manufacturers will continue to copy errors from existing PCBs. Unfortunately, in fact, there is this practice of copying parts of existing boards without thinking or having a clear idea of ​​what you are building, so it's very common in homebrew machines to find redundant lacks and flaws.

Based on the wiring diagram of the original 1chipMSX machine, I have implemented this new hardware patch for Zemmix Neo which allows to stabilize the +5V input line. Therefore, if you are experiencing instability in your Zemmix Neo machine, this solution can solve your problems. This patch can for example remove some annoying video interference on the output of GFX9000 and other similar cartridges. For the moment I have tested this modification only on the Zemmix Neo Brazilian pcb...

WARNING! Do this at your own risk, you will be solely responsible for any damage to your hardware.

It is in the nature of homemade products but not at all in the MSX. On the contrary, MSXs go through the years better than most other computers.

KdL,
Thanks to you, OCMs have become credible solutions for a large part of MSX users.

The "original" Zemmix Neo from Korea,has this problem too?
Thanks KdL

Please be informed that the problem is currently only present on Zemmix Neo Brazilian and not with Zemmix Neo Korean, but this fix can still be used if your hardware is unstable. I assume the instability is due to the lower quality of the dc-dc converter used on the Zemmix Neo Brazilian.

On the Spanish Zemmix neo I have seen some approaches to replace the missing only-Korean DC-DC converter part SPD1R5, with a SUCW1R50512C(Cosel), or an IH0512D(XP-Power) in my own case.

I have no such problems of +5v stability, but it is a good idea to add the capacitor.

The only problem is.... the pin-out is totally different....

This can aid you, the pin-out of the SPS1R5(up to date version with better characteristics):

Here's a quick feedback about KdL power supply fix: I also had video interferences on the VGA/RGB output of my Zemmix Neo (not only with GFX9000). I did not noticed them on a CRT, but when plugged on a big QLED TV through an OSSC, these interferences were quite visible.

So I tried KdL fix and added a 470uF capacitor like described: things were better, but the interferences were quite visible.

I then tried to change the external power supply block with another old (massive and transformer-based) 5V power supply: no more interferences at all

I'm not sure if the power supply I had on my Zemmix was the one sold with the Zemmix (no brand on it, but the serial number is "ycz-0528").

Later I also tried another modern (switching) power supply, and no interferences either. The only problem with this one is that it's only 0.5A, I'll need to find something a bit more powerful.

So it looks like there's also an issue with this "ycz-0528" power supply (maybe not only with the Zemmix internal DC-DC converter).

I am using a generic +5V 2.5A switching power supply for all of my tests. With 1chipMSX and Zemmix Neo Korean no problem, only the Brazilian version has those interferences. Using the 470uF capacitor I improved the image of the GFX9000 but did not match the quality of the other two machines. A power supply below 2A is not recommended.