rb@ccivax (01/17/86)
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