800XL unknown RAM upgrade

[ClausB]

26 minutes ago, reifsnyderb said:

once I lay out the board. 

The two LS157s are wasteful. They could be replaced by a single LS153.

[reifsnyderb]

I laid out a board and verified the connections are where they should be.  A couple mistakes were found.  Here's the updated schematic.

 

[reifsnyderb]

Here's a couple board pictures.  I used the top side to replace the wires with lands.  Also, I added solder points.

 

 

[TZJB]

On 1/26/2023 at 11:25 AM, Mclaneinc said:

Ah, could not see them / didn't notice them..

 

Thanks..

You are correct, the DRAM is completely obscured by the EMMU board but we can just see one in a couple of pictures, 8 x 41256 150nS for 256K.

[+af0l]

1 hour ago, TZJB said:

You are correct, the DRAM is completely obscured by the EMMU board but we can just see one in a couple of pictures, 8 x 41256 150nS for 256K.

That's my fault entirely, the pics are really sloppy. Sorry about that.

[+af0l]

2 hours ago, reifsnyderb said:

Here's a couple board pictures.  I used the top side to replace the wires with lands.  Also, I added solder points.

 

Darn, your skill is unquestionable, Sir.

 

So, the verdict? should I see the entire 256k or is 192k what I shoud expect here?

[_The Doctor__]

64 base 192 extended total of 256 if implemented fully, and as was also noted, a possible hidden switch via joystick port that may or may not be latched. I don't know if it needs to be held constant or just during power up. It would be nice if it does but if it didn't latch it would be nice to modify to do so. That way you could select at power up and then use the joystick as usual.

[reifsnyderb]

2 minutes ago, _The Doctor__ said:

64 base 192 extended total of 256 if implemented fully, and as was also noted, a possible hidden switch via joystick port that may or may not be latched. I don't know if it needs to be held constant or just during power up. It would be nice if it does but if it didn't latch it would be nice to modify to do so. That way you could select at power up and then use the joystick as usual.

The joystick port setting would have to be held constant.  That's why I think that somebody, in the past, had a toggle switch connected to the joystick port.  If 192k is being used, and a second joystick is being used, I would expect memory problems.  Ideally, it would latch on bootup only.  However, there's nothing in place to set a latch.  There is a spare latch on the 74LS74, however.  It may be possible to hack the extra 74LS74 latch into the circuit so as set the latch on a reset.

[TZJB]

10 hours ago, af0l said:

Darn, your skill is unquestionable, Sir.

 

So, the verdict? should I see the entire 256k or is 192k what I shoud expect here?

You seem to have 256KB of total memory on the board, 64K of which is preserved as the original primary bank and the rest as extended memory as @_The Doctor__ said. Presumably selected by the PIA as 16K banks similar to Atari XE banking, up to the maximum of 192KB.

Edited January 28, 2023 by TZJB