At 10:38 20.11.2001 -0800, Duane Maxwell wrote:
>I'm suprised you got something illegal - the BBS7 instruction is a 65C02
>instruction, but the ROM specified is for a II+, which used a 6502.  Perhaps
>some other instruction is busted.

Hmm, maybe.  A ROM listing would be helpful, but I'll see if I can trap on 
the previous instruction(s).

OTOH, maybe it's something in my image -- feel free to try HPLOT TO 10,10 
in a freshly powered-up emulator, and see what you get.

> > That is, a combination of INC and SBC (sometimes called "ISB").
>
>Actually, BBSn zp, adr is BranchOnBitSet, which tests bit n of the zeropage
>location zp, and branches to relative address adr if it's set.

Agree on the 65C02.  On the bare 6502 though, it was indeed an undocumented 
instruction with the described effect, IIRC.  I'll have to dust off my 
SYM-1 to run some real tests.

>Note also that this stuff is painfully close to Slang....

Sure made me move up my PDP-8 emulator a couple of notches on the task 
list. ;-)

Cheers,
Helge

P.S. All this on the same day that I learnt that the CP/M-80 sources are 
disclosed at <http://www.cpm.z80.de/index.html>...