Chip Select for 8 MB based DIY cartridge doesn´t operate well

[mst0mst]

Greetings MiGeRA,

First, congratulations for the great FlashMD software and kit!

I managed to build a 8 MB flashable cartridge using a MX26L6420.
Thanks to FlashKit programmer hardware its possible to flash
and read correctly the entire 8 MB of the flash chip,

The problem comes when I try the cartridge in a real hardware
target, a first model european MD; the game flashed in the cartridge
doesn´t operate at all (black screen) if B26 is used as chip select (CE) signal.

However, cutting the PCB trace and soldering a wire to B17 (classic CE signal),
lets the game to start correctly, but obviously only the first 4 MB can be accessed
by the console´s hardware, if I try to use a sprite placed beyond the first 4 MB limit,
only 0xFF are returned for any read data, due to chip select signal is not generated
over first 4 MB space in B17

The game uses linear addressing, not banked; I prefer to stick to 8 MB linear space,
is a good amount for a good modern game, and linear addressing has the benefit
of easier game coding. Banking is a mess and makes hard to reuse a lot of graphics.

Is there any altenartives to create a suitable CS signal for entire 8 MB space, using the minimal amount of components?

Thanks in advance,

[MiGeRA]

Greetings you ;-)

Of course, alternative is has. For example, you can always and for any case organize manual address decoding (full or partial) - but there is a problem with the elegance and simplicity of the solution, because requires the use of additional parts.

But our case is trivial, try using line A23 (pin B11) as CE for Flash-ROM (when used in hardware sega).

Well, to be sure, also check the memory power supply. The programmer is less picky and creates better power for the cartridge than real ancient equipment. You must try increase the rating of the Flash-ROM shunt capacitance, also try used dc-dc convertor ex. HT7536 ...

[MiGeRA]

The option I proposed above might look like this.
Please pay attention to the need for high-quality power supply for this microcircuit: I used a 3.6V stabilizer (7536-1, suitable for pinout), and also the capacitors will be very useful 4.7uF two pieces (tantalum).