RF08/RS08 emulation

Vincent Slyngstad vrs at msn.com
Thu Aug 7 17:29:01 CDT 2008


From: "Ethan Dicks" 
> On Thu, Aug 07, 2008 at 02:27:19PM -0700, Vincent Slyngstad wrote:
>> No particular reason, but the board's pretty crowded trying to get 
>> it all to fit in 8"x11".  I'd probably use SIL resistor packs and 
>> shift down the six DIPs below the switches.  (I'm not sure there'd 
>> be enough void left to route the thing with 10mil design rules.)
> 
> Sounds crowded.

It is a little.  The 8"x11" restriction is really just to keep the 
prototype cost low for a particular board shop.  If that or the 
10mil restriction were relaxed, things would get easier.

Of course it would also be fairly easy to redo the thing with 
GALs instead of TTL, which should also make it easier to fit 
things in, but would require me to program parts.

>> There's some other "fast and loose" stuff in there too -- S240 as 
>> bus drivers, multiple LS loads on the bus (still should be less 
>> than a 74xx load), and (importantly) no provision to continue the 
>> bus, so that it must be placed last.  There's also no equivalent 
>> for the G717 terminator card, so it may need to be a fairly short 
>> bus!
> 
> Well... while that's not optimal, it's workable.  Given the dearth
> of OEM posibus equipment these days (I have none and have never
> seen any except on the web), it's not like many people are going to
> be sticking this on a heavily loaded bus.  The RF08 is large enough
> to do interesting things with, leaving only removable media to get
> things on and off the system - paper tape is certainly one way,
> but floppies are more convenient... in my particular case, I suppose
> the largest configuration I'd attempt would be a modern solid-state
> RF08 and that RX8 you/we started and haven't gotten back to.  It's
> been so long that I can't remember if the RX8 can be in the middle
> of the posibus or not.

The RX8 will go in the middle of a bus, and even has a provision for a 
G717 equivalent bus terminator, in the form of an optional SIL resistor 
pack.  Real drivers, too.  Of course, being known not to work as yet, 
I doubt anyone will be rushing out to build it :-(.

    Vince




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