I have a couple of LCD displays that are internally configured for 8080 bus and have no provision for 6800 bus even though the controller used has this option. Seems the manufacturer decided 8080 was the best choice! Not a smart move in my books. )
Anyway, does anyone know a simple and easy way to generate the RD and WR bus signals from the Netburner's 68000 bus signals?
The only Netburner signals I have available on the external bus connector are as follows: (with a redesign of the main PCB which I would prefer not to do)
R/W
OE
CS
A1
D0-D15
Appreciate any thoughts. I have tried searching on Google and I used to have a circuit from an old 6502 based design before but I can't find it now.
If i remember correctly, you will need glue logic to invert the R/W to become an active low R singnal and then "or" it with the OE signal so that it is low only when R/W and OE are both low. You will also have to "or" the R/W directly with the OE so that the W is only low when both the R/W and OE are low.
You should be able to do it with a single chip quad nand gate.
There are a few ways you can do this. If you don't mind using two chip selects and reading and writing to different address ranges then this can be done without extra logic. The quad UART IC we use for the PK70 blade board also has this type of bus. What we found to work here was using 2 separate chip selects, one for /IOW and one for /IOR. The tricky part was generating the 4 CS signals for the 4 UARTs. After some experimenting we got this to work by using address lines A3 and A4 into a mux to provide the 4 chip selects. Since you probably only have one CS you should be able to just use the /TIP signal for your single CS signal.
)