External KERNAL using a 6510

Date: 2000-08-29 22:19:50

Hallo allemaal,

Reading the German RUN of March 1987, I run into an article about how to
connect an external Kernal to the expansion port. The most interesting
thing was that it used a 6510 (yes, the processor) as part of the
construction. No, it was not meant to replace the original one. There was
no diagram given so I had find out how everything was connected by looking
at the layout and what the text said.

AEC is connected to GND, tristating the 6510 permanently. (The text says
only the addressbus). 
RDY is connected to BA (text: for tristating the databus when needed). 
The inputclock is derived from CLK2 from the bus using a 74LS121.  
With the exception of CLK2, the rest of the pins is connected with their
counterparts on the port.
A 74LS30, 8-input NAND, decodes P1, CLK2, A13..15, BA, R/W and a line that
disappears into the blue; it goes and goes over the board but is connected
to anything. (The whole layout looks as if it could be used for more
purposes because there are much more lines and holes not used) The output
enables the EPROM and pulls EXROM (L) thru a diode. 

My only opinion is that they use the 6510 as a giant decoder for address
$0001 with build-in I/O. But if this is the case, why not using some, much
cheaper, gates and a latch like the 373 or equivalent? 

Some minor details:
- They claim that this design has no compatibilty problems at all. Next
sentence: maybe with some "poor build" 80-character cards and Prologic-
DOS 1. (org: unglueklich gebauten)
- Next sentence: the external Kernal is located in "abschaltbaren" ROM (=
can be disabled) Except for that line running into the blue, I did not find
a way to disable the external ROM. 
- My first thought: where could you get a loose 6510 in those days for a
reasonable price? I think thay costed about $40 at that time.

If this construction works or not, the fact that they used a 6510 in this way 
completely suprised me. I wonder how you feel.

Groetjes, Ruud

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