Re: Vector rotation

You wrote:
> On Tue, 15 May 2001, Paul Kahler wrote :
> > Technically ANY branch instruction can be used to select the
> > secondary accumulator, but it's not used that way much if at all.
> >
>
> Do you mean *any* as in any opcode dealing with a branch or those with
> that one particular bit set (bit 3 I believe)? Sorry if I seem nitpicky
> here...just
> curious. If I am not mistaken opcodes 0x50 to 0x57 were the branch no
> select accum B and 0x58 to 0x5F were branch + select accum B.
>
> I'm just concerned that you might be able to select the other accumulator
> doing a branch based on some previous instruction. I kinda got that hint
> from your post....

That sounds correct. That bit in opcode 5x sets the "secondary" flag
so the following instruction will operate on the "other" accumulator.
This is the only way to select it, and it only stays selected for 1
instruction. It happens if the branch is taken or not. The other 3 bits
go to a mux to select the branch condition - there is a free pin there
to add another condition. It seems like one of them goes to a connector
and that TG used the XY D/A to generate a voltage and used a comparator
to compare to analog sticks and feed it into that condition bit. This
is used to do successive approximation A/D conversion on the stick.
TG also has support for digital 8-way sticks - it's DIP SW selectable.

SeeYa,

-- 
<pre>
 ___   __   _   _  _
|   \ /  \ | | | || |       phkahler@oakland.edu     Engineer/Programmer
|  _/| || || |_| || |__     " What makes someone care so much?
|_|  |_||_| \___/ |____)      for things another man can just ignore. " -S.H.
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