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[XavSnap]

[XavSnap]

Hi!

I plan to install the RomCs decoder.
But, there's something wrong.

There is a RomCs on the zx81's edge connector.
Where is it located?
After the R28 resistor (Rom side) or before (ULA) ?
This resistor seem to be used to pull down the ROMCS to 0v on the edge conector... and disactive the main Rom...
But, in my tweek, this resistor is removed !
If the edgs conector's /RomCs is wired to the 0v, the 74Ls32 is shortcuted... and will be destroyed !
I had to install a disk driver on it, and i don't know if the RomCs will work on this tweeked computer!
It's same regard the Ram controler...

A serial resistor (R28) beatween our new /RomCs and the ROM/edge is needed !

note: the edge connector connections aren't display on the ZX81 circuit diagram...

Have Fun !
Xav.

[siggi]

Hi!

I plan to install the RomCs decoder.
But, there's something wrong.

There is a RomCs on the zx81's edge connector.
Where is it located?

After the R28 resistor (Rom side) or before (ULA) ?

After the resistor (Rom side)

This resistor seem to be used to pull down the ROMCS to 0v on the edge conector... and disactive the main Rom...

It is normally used by external components (e. g. an address decoder for an external EPROM) to pull the /ROMCS-input HIGH to disable the internal ROM.

But, in my tweek, this resistor is removed !
If the edgs conector's /RomCs is wired to the 0v, the 74Ls32 is shortcuted... and will be destroyed !

Add it between the output of the LS32 (ram control LS32 (pin 8) or ROM control LS32 (pin6) : that pin, which is directly(!) connected to the ROM-socket /CS-pin) and the edge connector pin (= ROM /CS). So an external component can still disable the internal ROM without destroying the LS32 (protected by your new resistor).

HTH Siggi

[XavSnap]

Many thanks Siggi,
We can keep the R28 resistor as is !
Ok.