Re: New CBM-II discoveries

I'm looking at the schematic, trying to understand it.Each bitplane uses eight 64Kx1 drams and the hardware can address a single bit from each plane.I agree... It can then write the colour in a single operation. That colour is set via the 6523 Port A - 3 bits for the colour and 3 bits enable writing. I'm not sure why you wouldn't always write the 3 colour bits but maybe I just haven't figured that out yet.
It looks like we CAN'T replace the 64Kx1 drams with 64Kx8 due to the method used by the EF chip to select individual bits. So not much chance of reducing the parts count. In fact it would be trivial to ADD additional bitplanes to make it support more colours. Imagine having 8 bitplanes and doing 512x512 pixels with 256 colours per pixel !
Steve

      From: smf <smf@null.net>
 To: cbm-hackers@musoftware.de 
 Sent: Monday, June 25, 2018 4:24 AM
 Subject: Re: New CBM-II discoveries
   
On 24/06/2018 02:32, Steve Gray wrote:

> you probably need to repeat the same draw command with a different plane selected corresponding to the on bits of the desired colour.

Using one port on the 6523 you can select which (any or all) of the 
drams will receive write strobes.

The data in on each chip has an or gate, which is fed by another 6523 port.

There is some RMW stuff going on that I don't understand.

It is likely you can draw colour in one operation.