Hi Christian, that makes sense indeed, I was too lazy to actually check a 2316/2716 datasheet and the schematic seemed to imply I could put a 2532 in UD8 too. So the 2001N addressing is much similar to the 2001, it doesn't have I/O shadows each 256 bytes but it can't use the "free" addresses for ROM. Now it makes sense of course. Yes it would be much better to put the I/O ports at $88xx, I can't even imagine why they didn't that in the first place. Maybe someone foresaw a case for expanding the video RAM to 4K in 1977? On Mon, Apr 16, 2018 at 5:49 PM, Christian Dirks <Toast_r@idealine.info> wrote: > Pin 18 is /CS2 on the 2316 ROM and the 2516/2716 EPROM. > On the Mainboard, Pin 18 is Connected to A11. > It works unless you try to use a 2332 / 2532, > which will give the named conflict. > > The reason for not using the x8xx signal to blank out only the 256 byte > I/O window from the /CS for UD8 seems to be, that orignally it was > planned to use another memory configuration, which eventually was > abandoned to be compatibile with the orignal PET: > On page 1 of the schematics (upper right, next to the memory expansion > connector) you can find a jumper for a signal named I/O. > It allows to move the I/O adress window from E8xx to 88xx. > In this configuration, a 2332/2532 can be used for UD8. > This memory configuration would have been much more flexible, it would > give a continous ROM area from $9000 to $FFFF without the I/O window in > between. > > Christian > > > Am 16.04.2018 um 14:15 schrieb Francesco Messineo: >> Hi All, >> looking at 320349 2001N schematics on zimmers.net I can't really >> understand how the I/O space addressing don't make a data bus >> conflict. >> On schematic 4, the UD8 select is directly connected to /SELE, which >> is low from $E000 to $EFFF, so UD8 must hold the databus even during >> $E8xx accesses. >> UD8 databus, like all other ROMs, appear to be directly connected to >> 6502's databus, without buffers. >> What am I missing? In the original 2001, there was no ROM mapped from >> $E8000 to $EFFF, but in 2001N, the I/O chips are addressed with both >> /SELE and X8XX signal that decodes (as the name suggests) >> A11,A10,A9,A8 = $8. >> I feel stupid, I know that 2001N works in real life, I have one >> myself, but I can't think that schematic is correct. >> >> Frank IZ8DWF >> > > > -- > Christian Dirks > Toast_r@Idealine.info > Vorster Str. 66 > 47918 Tönsivorst > > 2. Stellv. Vorsitzender > Verein zum Erhalt klassischer Computer e.V. > http://www.classic-computing.de/ >Received on 2018-04-16 21:00:02
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