------------------------------------------------------ From: Clockmeister > > On 11/03/2014 4:30 AM, silverdr@wfmh.org.pl wrote: > > When trying to deal with some 4168 XRAM chips, I couldn’t get them to work properly. After > studying the datasheet I found in the notes: > > > > http://dl.dropboxusercontent.com/u/58002657/4168_notes.jpg > > > > Point [2.] seems important to me but I seem to have problems interpreting it unambiguously.. > or for some other reasons these RAMs still don’t want to work.. > > > > “An initial pause of 2ms is required after power up, followed by any 8 _CE cycles and 64 > _RFSH cycles before proper device operation is achieved. Read, write, and external > refresh cycles may be used as _CE dummy cycles for initialisation. The 64 refresh dummy > cycles can be performed before or after the 8 _CE dummy cycles. Both dummy cycles must > be within AC parameters. See figure 1, below." > > > > Figure follows as on the picture linked above. How do you understand the above? How should > it be interpreted? Please note that e. g. here: > > > > http://www.smspower.org/uploads/Development/SegaMasterSystemIIServiceManual-1715922A-1.png > > > > the _RFSH is tied up to VCC.. > > I'm sure I've replaced these with standard SRAM (and/or vice-versa). > When you say they don't work, what are you trying to get them to work in > and in what way don't they work? Some time around the middle of last year I had an idea of doing exactly what you wrote. I wanted to put XRAM in place of SRAM onto my DD2 and DD3 boards because I have a good bunch of those 4168 XRAM chips that lie unused (taken off a working industrial equipment during scrapping). But they don’t work in the sense that the system hangs when I put the XRAM chip. I tried doing the same as on the RAMBOard, i.e. connecting _RFSH to PHI2 and adding one more cap for delaying the _OE/_CE lines. I even connected CS to PHI2 as in the RAMBOard schematic (just to be sure) but it still didn’t help. After scratching my head for a long time I eventually found the note in the data sheet that made me suspicious whether I shouldn’t be doing something extra to make them work.. -- SD! Message was sent through the cbm-hackers mailing listReceived on 2014-03-11 12:01:55
Archive generated by hypermail 2.2.0.
