Anyone playing with the 8x300 - test-drb@ccmp.vtda.org

14 May 2005

...
 From: "Allison" <ajp166 at
bellatlantic.net>

Subject: Re: Anyone playing with the 8x300
   From: "Dwight K. Elvey" <dwight.elvey at amd.com>
   Date: Fri, 13 May 2005 14:57:09 -0700 (PDT)
     To: cctalk at classiccmp.org

Ah the classic first of the fast microcontrollers.
I'd have to dig but I vaguely remember the 8x300
as a disk controller apnote.  Nasty beast to program.

Allison

Hi
 Don't know why you'd say this, it only has 8 instructions!
I've got the spec posted to Al's site.
 This controller application is a little interesting in that 
who ever designed this board, also must have done a bitslice
designs at one time or another. To save a machine cycle, all
I/O addresses are selected by a ROM tied to the instruction
addressing. Normally it would take two cycles, one to write
the I/O address and one to transfer the data. With the
ROM, the address is understood by the program's execution
address location.
Dwight 
It's more of a sequencer or state machine with a crude ALU.
As to those 8 instructions, looks at what the fields are 
for each one. I've done horizontal microcode and that is 
similar. Due to it's very harvard design it's not one you 
will do constans in rom much.  Also the IO devices are 
really IO specific as in the address of each is coded 
into the part.  
Hi Allison
 It is interesting that this application didn't use
that method of I/O addressing. All I/O devices are typical
bus type devices. It has a ROM connected to the instruction
addresses that selects the I/O based on the address being
executed. They don't seem to be taking advantage of the
read modify write I/O, either. The ports are all wired as
unidirectional ports.
Dwight

...

One use for it was an 8bit wide DSP.  I have a real one here
of the later 8x305 I2L that was a bit faster.

Allison