External and internal data width

[jeffythedragonslayer]

The Wikipedia page about the 65816 has an infobox containing this:

Quote:

Data width
8 (external)
16 (internal)

External and internal to what? Is it trying to say that memory is fetched from RAM in 8 bit chunks but registers inside the 65816 are 16 bit?

[drogon]

jeffythedragonslayer wrote:

The Wikipedia page about the 65816 has an infobox containing this:

Quote:

Data width
8 (external)
16 (internal)

External and internal to what? Is it trying to say that memory is fetched from RAM in 8 bit chunks but registers inside the 65816 are 16 bit?

Essentially yes.

There are flags to run on/off the 8/16 bit access/transfer mechanisms, so it can all by 8-bit or all 16-bit or some 8 and some 16 but when reading or writing a 16-bit value from RAM, then 2 RAM accesses are needed.

-Gordon

[GARTHWILSON]

jeffythedragonslayer, yes; in native mode, you can set the accumulator to 8 or 16 bits, and you can set the index registers to 8 or 16 bits. So if you have the accumulator set to 16 bits wide for example, and you do an LDA foobar, it will put the byte at foobar in the low 8 bits of the accumulator, and in the next cycle grab the content of foobar+1 and put that in the high 8 bits of the accumulator. INC foobar will do a 16-bit (two-byte) increment of the variable at foobar. See my article about the common misunderstandings surrounding, and the attractions of, the 65816.