Hey, English blokes...what's an Apricot? - test-drb@ccmp.vtda.org

7 Jul 1998

...
  [8089]
>> (very fancy DMA chip).  
...
 > Thats like naming the Newton a fancy post it
thing. The
> 8089 was a full featured CPU, just with an special
> command set suited for I/O operations. Anything from 
...
  True. I've got the 8089 data sheet, and a 3rd
party '8089 I/O processor 
 handbook', and it is indeed a coprocessor. However, it's normally used 
 (and it's used in the Apricot) as a DMA controller, so it's best to think 
 of it that way, for all it can do a lot more. 
...
  It's a lot nicer than the 8237 used in the IBM PC.
For one thing it 
 correctly handles the 20 bit address bus, so there's no problem with 
 crossing 64K boundaries. For another, it can monitor a Data Ready flag on 
 one port, and transfew data when the peripheral is ready. No need to have 
 DMA channels in the PC sense. 
...
 > serial I/O via disk I/O up to code translations
could
> done in a very smooth and genuine way.  
...
  Howver the Apricot has a normal serial chip and disk
controller, and only 
 uses the 8089 for DMA. 
Maybe I used the wrong words - poor english language skill -
Of course a regular Serial I/O chip is still needed, the
8089 has no serial (or what ever) I/O of its own. But instead
of the main CPU, the 8089 will respond to all requests
for data transfer  - shure, you could use two DMA chanals
for input/output data, but in difference to an ordinary DMA
the 8089 could also handle the status lines and drive a non
hardware protocoll - from xon/xoff up to HDLC. Same for any
other kind of I/O hardware, not only serial, since the logic
is software not hardware.

Gruss
H.

--
Ich denke, also bin ich, also gut
HRK