On Saturday, Dec 13, 2003, at 12:19 US/Pacific, Herbert Graf wrote:

>> And of course the famous "sex" instruction.
>
>         Now this peaked my interest, what "sex" instruction? Executing
> it would cause the chip to get up and seek a mate?

"SEt X"  The 1802 had 16 16-bit pointer registers, and several 4-bit
registers that selected which of the pointer registers was the PC (P),
and which was the data pointer register (X)  You could also reference
a data pointed to by a register via the instruction itself, or via the
designated PC (which gave you immediate data capability.)  There were
assorted autoincrement and decrement modes.  DMA, input, output, and
most math all went via memory pointed at by a register.  The 1802 was
pointer intensive in exactly the way that a PIC isn't. :-)

The canonical "call" procedure consisted of designating standard PC
and stack registers, and setting the PC pointer to a register that
would hold the address of code that would push the normal pc onto
the stack, grab data from the old pc (with increment to get beyond
it), move that into the standard pc register, and set the pc pointer
back to the standard one.  Short calls consisted of simply switching
which register was the PC (but you couldn't nest those...)

It was ... neat.  Wish I had gotten around to building one :-(
(I DO still have some 1802s in my junk box.  But I've sorta lost
the love of toggling in programs...)

BillW

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