Last Updated or created 2024-06-08

First setup to make an address decoder for my 68k

000000 - 007FFF 32k * 16 bits RAM
F80000 - FBFFFF IO0,1,2,3,4
FF0000 - FFFFFF 32k * 16 bits ROM

We need /LDS and /UDS for odd even select, because rom and ram are 8 bits chips.

Also we are not decoding all address lines.

x0xxxx - RAM
F8xxxx - IO
FFxxxx - ROM

This means there are blocks repeated

Address lines
23 22 21 20 19 18 17 16 .....
1  1  1  1  1  1  1  1  * ..... ROM
0  0  0  0  0  0  0  0  * ..... RAM
1  1  1  1  1  0  *  *  * ... IO but A17 A16 are sub selects

Code for ATF22v10
Not used yet! .. not verified!

-------------
GAL22V10
68000addr

Clock   A23   A22   A21   A20    A19   A18    A17    A16    LDS  UDS   GND
/OE   ODDRAM   EVNRAM  ODDROM    EVNROM    IO0    IO1   IO2    IO3   NC   NC VCC


/ODDRAM = /A23 * /A22 * /A21 * /A20 * /A19 * /A18 * /A17 * /A16 * /LDS
/EVNRAM = /A23 * /A22 * /A21 * /A20 * /A19 * /A18 * /A17 * /A16 * /UDS
/ODDROM = A23 * A22 * A21 * A20 * A19 * A18 * A17 * A16 * /LDS
/EVNROM = A23 * A22 * A21 * A20 * A19 * A18 * A17 * A16 * /UDS
/IO0 = A23 * A22 * A21 * A20 * A19 * /A18 * /A17 * /A16 * /LDS
/IO1 = A23 * A22 * A21 * A20 * A19 * /A18 * /A17 * A16 * /LDS
/IO2 = A23 * A22 * A21 * A20 * A19 * /A18 * A17 * /A16 * /LDS
/IO3 = A23 * A22 * A21 * A20 * A19 * /A18 * A17 * A16 * /LDS

DESCRIPTION
A 68000 addr decoder
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UPDATE

I’ve got some K6T4008C1B RAM chips now.
These are 512k, but I don’t need that much (for now)
So I’ll still use above decoder and below schematic