Re: 16 bit data bus on a 6502.

>You don't do it this way when talking to a 8Bit I/O-chip. 16Bit-CPUs
>have commands that only output 8 Bits. If the I/O-Chip is 16 Bit wide,
>then all 16 Bit will be transfered at the same time with 16 Bit I/O
command. 

That's the thing... trying to talk to a 16 bit memory chip by splitting the
16 bit data between the actual data bus and the 8 bits parallel port.

My theory is:

- Wire the MSB of the 16 bit RAM chip data bus to the parallel port of a PIA
like the W65C21.
- Wire the LSB of the 16 bit RAM chip data bus to the data bus of the 65816.
- Wire the 65816 address bus as usual, to the address buses of the other
chips.

So when wanting to write a value to the 16bit RAM chip, the programmer would
first put the MSB in the parallel port, and then write the LSB to the memory
location.

This last write would enable the /CS and /WE lines of the 16bit RAM chip,
that would already have present the MSB value in its MSB lines thru the
parallel port.

*BUT* I don't know if the parallel port would had the MSB value there,
latched until a new value would replace the existing one, or if the parallel
port would discard the MSB value after a while.



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