🚀 go-pugleaf

I have been wandering if it would be possible/safer/easier to use a separate
PC-Board(s) (Like one or two of those RAM boards from Radio Shack)
and reduce the amount of hardware wiring required.

> Step  6: Orient the 520ST PCB so that you are looking at the
> solder side of the PCB (non-component side), with the row of
> d-rams  nearest  you. Find the double square pattern of pads
> at the 68-pin socket of the memory controller, U15 (3H2119).
> The  following  is  a  guide  to  locating  the  six  memory
> controller pins necessary to complete the wiring. The socket
> is numbered conterclockwise, starting with pin 1, the square
> pad  (look closely) in the middle of the bottom outside row.
> The  sequence,  moving counterclockwise from pin 1, first on
> the  outside  square ONLY: (NOTE: the sequence ")(" means to
> make  a  90-degree  turn  counterclockwise,  i.e. around the
> corner)
> 1,3,5,7,9)(10,12,14,16,18,20,22,24,26)(27,29,31,33,35,37,39,
> 41,43)(44,46,48,50,52,54,56,58,60)(61,63,65,67
> The  sequence,  moving  counterclockwise  along  the  inside
> square  only,  and starting with the left side of the bottom
> row:
> 
> (62,64,66,68,2,4,6,8)(11,13,15,17,19,21,23,25)(28,30,32,34,3
> 6,38,40,42)(45,47,49,51,53,55,57,59)

I assume from the "Unix without MMU" discussions that this is really
more of a DRAM-Controller and Multiplexor chip (Like the 6883 on
CoCo's) is there any mapping/segment capability?  Anyone figured
out how to create one in "gate-arrays" or something?

Is it possible to get more information about the other pins on
this chip?  Which ones are the address/data/control?
Are there any pins (molex header?) that could be used to tap
in the extra memory?


> Six 68-ohm 1/4W plus/minus 10% carbon film resistors must be
> added when adding memory. These series terminating resistors
> minimize undershoot which may damage BOTH BANKS of d-rams if
> omitted.  Solder  a  68-ohm resistor to pin 18 of U15, RAS1.
> Solder a #24 AWG stranded wire from the remaining end of the
> 68-ohm  resistor  to  the  pin  4  bus  (RAS) of all the new
> d-rams. that is the new U16, 17, 18, 24, 25, 28, 29, 30, 32,
> 33, 34, 38, 42, 43, 44, and 45.
> 
> Solder  a  68-ohm resistor to pin 22 of U15, CASH1. Solder a
> #24  AWG  stranded wire from the remaining end of the 68-ohm
> resistor    to    pin    15    bus    (CAS)   of   the   new
> U45,44,43,42,38,34,33,32.
> 
> Solder  a  68-ohm resistor to pin 21 of U15, CASIL. Solder a
> #24  AWG  stranded wire from the remaining end of the 68-ohm
> resistor   to   pin   15   bus   (CAS)   of   the  new  U30,
> 29,28,25,24,18,17,16.
> 
> For  best  results in all three cases above solder the wires
> coming  from  the  resistors  to the middle of the three bus
> wires in a "T" fashion rather than at one end of the buses.
> 
> Use  a  continuity tester to find the following three traces
> --  do  not  depend  on visual inspection. Now install three
> 68-ohm  series  terminating  resistors  in the original 512K
> bank of ram. Be very careful while soldering to these narrow
> traces,  since  excessive  heat can easily lift a trace from
> the  board. Use an Exacto knife to gently remove solder mask
> from traces.
> 
> Cut  the  trace  leading  from pin 8, RAS0, of U15 near U15.
> Solder a 68-ohm resistor in series with the trace.
> 
> Cut  the  trace  leading from pin 6, CAS0H, of U15 near U15.
> Solder a 68-ohm resistor in series with the trace.
> 
> Cut  the  trace  leading from pin 7, CAS0L, of U15 near U15.
> Solder a 68-ohm resistor in series with the trace.

Are these series resistors being installed in newer boards?

Does Atari provide an internal RAM-Expansion header like the
one in the old Sanyo MBC-550?

Has anyone on Compuserve heard any more about the "ram expansion board kit"
discussed back in November?

Is Atari Still Reading This Net?


rb@ccivax