Re: ProDEV DDT debugger?

[aiiadict@gmail.com]

DDT8 should be easy to build.

I did some google searching, and got a full feature
list.  You could build the breakpoint feature into a card
with an AND gate, some 7404 inverters, and dipswitch
block or toggle switch.  Set the address to BREAK
at with the switches, tie the output of the AND gate to
the INT pin on the slot.  Put your own interrupt handler
in RAM.

Button causes interrupt:  Pushbutton to the INT line
on the slot.

"realtime ROM breakpoint" I don't really understand
this one.

last: hardware timer.  It mentions that Prodev will
count number of cycles required to execute code
between two addresses.  I don't understand why
you would want this, it can be done in software.
But, You have to detect start address on the
bus.  count, synched with apple clock, detect
end address on bus, stop the count.  The count
has to be available on the bus.  Doesn't sound
very hard to get done.

You can use the same circuit from the breakpoint
above.  Have the ouput of AND gate go to START
on hardware timer.  Put a toggle switch from the AND,
so it's output will either go to INT line or timer START.
I think 6522 has built in timer that would work.

You need a second AND gate, some inverters.  Toggles
to select which address.  The output of that AND gate
goes to timer stop.  You need another address decoder
so you can read the time from the Timer chip.  When
that address appears on the bus, along with R/W at
correct level, you connect timer data lines to data
bus.

I think you could do it for about $30 of parts, and
maybe 2 hours of work.

Rich