Anyway, on the universal board, $Exxx ROM is selected by /SELE and X8XX combined, so one could use a 2532 ROM in place of the 2316 and add some code too. On Mon, Apr 16, 2018 at 8:46 PM, Francesco Messineo <francesco.messineo@gmail.com> wrote: > 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 23:03:11
Archive generated by hypermail 2.2.0.