r-time 8 cartridge

[HiassofT]

Thanks. I'm gonna look thick here, but I'm still getting my head around the whole address decoding thing, and I like to understand things fully. I understand A4-A7 are the high nibble bits in the LSB of a sixteen bit address. Obviously we're interested in the low-nibble as an offset from $D500 in this case, which I assume is selected by the CCTL line when the address bus refers to anything in the $D500 page. Obviously the MyIDE cart already has A0-A3 wired up to its own decoder chip.

The original MyIDE cart doesn't do any address decoding at all. It only uses the CCTL line (D5xx) from the cartridge port to check if the r/w access is in the $D5xx page.

 

It passess A0-A2 to the IDE drive, which means that A3-A7 aren't decoded at all, therefore all IDE registers are repeating every 8 bytes ($D500 is identically to $D508, $D510, ... $D5F8).

 

With the second version of the LS138 circuit the following is happening:

 

/G2A (pin 4) is connected to A7, which means A7 must be low to enable access.

/G2B (pin 5) is connected to CCTL, which means only access to page $D5xx is enabled.

(G1 at pin 6 is connected to VCC, so this is always true and doesn't matter).

 

So far we have: page $D5xx and A7=low, which means $D500..$D57F.

 

Now the 3 inputs A-C (pin 1-3), connected to A4..6 are decoded by the '138 to 8 outputs.

 

Combined with the Gx inputs before we now have:

 

Y0 is activated (set to low) whenever $D50x is accessed (A0-A3 don't matter here)

Y1 is activated at $D51x

...

Y7 is activated at $D57x

 

The rest of the address decoding is done internally by the IDE drive (using A0-A2), A3 isn't used at all, so $D508 is the same as $D500 etc.

 

so long,

 

Hias

[flashjazzcat]

Thanks for the explanation. I'll do some further reading the datasheets. This is going to be useful.

[_The Doctor__]

so what is the bottom line here... I have the MyIDE 1 megabit maxflash cart... it hates my rtime 8 and gets in the way of things, What exactly do I need to do in order to make sure the interface cart has 100% speed and functionality... I don't want to lose the video playback or larger sector, etc etc.

Will status from ide and software reset mod interfere with anything else... like rtc black box mio etc.

[_The Doctor__]

I currently have the MyIDE flashed with FJC APT SPARTA using 512 sector and APT and fat access. I want to make sure I don't lose anything but can gain some compatibility