help - 11/34 console problem -- first LA output - test-drb@ccmp.vtda.org

8 Nov 2005

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

Subject: Re: help - 11/34 console problem -- first LA output
   From: "Chuck Guzis" <cclist at sydex.com>
   Date: Mon, 07 Nov 2005 20:18:21 -0800
     To: cctalk at classiccmp.org

On 11/7/2005 at 9:31 PM Allison wrote:

>Well save for wrap around.  The stack on 8008 is strictly address and
>as already said 14bits (the 8008 only addresses 16k!!) and 8 levels deep.
>It was a challenge programming it to figure out where you came from and
>also not blow the stack.  Still it beat the design we had before it as
>that was around 220 pcs of TTL sequential logic. 
Well my 8008 experience predates DEC and the TTL horror was pre 8008!

I'll say it this way.  The 8008 was a ground breaking micro.  From a 
programmers perspective it wasn't too bad but from a hardware designers
and debug perspective it was nasty.  It was enough to be a micro but as 
feature free as one can get.  However for the time it was pushing the
limit for integration at around 5000 transistors in Pmos.

The number of chips with limited internal stacks would amaze you.  The
8048/9 series is a fairly well known one, TMS1000 4 bitters, NEC uCOM4
4 bitters, NEC uCOM75 series, National COPs and even the PIC all come 
to mind.  And in every one them if you exceed the stack something falls 
off the bottom.  Stack red zone hardware is truly a big machine thing. 
Hi
 I thought I might add that many current day DSP chips also
have internal stacks. Of course the Forth chip, the NC4000
used external stacks but had 3 busses to handle them so that
one could have all being active at one time. Two were stacks
and one was for instruction/data.
 The 2100 family DSP by ADI has a limited internal stack as well
but it seems like I remember it would generate an interrupt if
it overflowed.
 Most tools for these have a method of indicating if the code
your running has a combination of main flow and interrupts
that would cause an overflow. Although, it doesn't seen so,
the worst case is predictable.
Dwight

...

 I always wondered why a carry or borrow from the
stack pointer couldn't
have at least generated a branch to some known location.  It may not have
exactly told you where your code went bonkers, but it'd be better than
letting the program run wild!  How many micros used a local stack?  The
Natoinal PACE is the only other one that comes to mind, but at least it had
a "stack about to overflow" interrupt and a way to access the stack
directly.

Were you a Datapoint employee?   
NEC and DEC but never Datapoint.

Allison