Re: [stella] Cart card edge connector

[Kevin Horton <khorton@xxxxxxxxxxx>]

At 20:18 9/3/01 -0400, you wrote:

> When I took the cart apart, the chip side of the board was facing up, so
> looking at the card edge with the chip side up, and looking at the pinout
> for the ROM chip (from, um, Kevin Horton's web site, I think?), I see that
> the chip's A11 line is wired to the card edge's A12 line, and the card edge's
> A11 line doesn't even have a pin... what gives?
>
> In fact, A0 thru A12 are present on the card edge connector... but this
> would allow for 8K carts, without bank switching. So is the FAQ wrong?
>
> I'm sure this has been discussed before on this list, I'm just trying to get
> clarification.. I *need* to understand this fully, before I break out the
> soldering iron.

Simple.  That's a 2K ROM, so it has no A11.  That "A11" on the chip is 
really the positive enable.  If you connect it to A12, it will be enabled 
when you are accessing the upper 4K of the total 8K address space.

A 4K chip has an A11, so you connect it to A11, and then A12 is still the 
positive enable. (All EPROMs have negative enables, so you must use an 
inverter (7404 or similar) to turn the positive enable into a negative one).

You can only use the upper 4K of address space, since the lower 4K holds 
the RAM, stack, TIA registers, etc. and is therefore unusable for code.


-
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/