Path: news1.icaen!news.uiowa.edu!news.physics.uiowa.edu!math.ohio-state.edu!howland.erols.net!newspeer.monmouth.com!intgwpad.nntp.telstra.net!news1.optus.net.au!optus!news.usyd.edu.au!news.uow.edu.au!david From: david@uow.edu.au (David Wilson) Newsgroups: comp.sys.apple2 Subject: Re: II+ vs IIe Char Gen PROMs and Shift-key mods-- LC $F8 PROM mod Date: 9 Apr 99 02:54:01 GMT Organization: University of Wollongong, Australia Lines: 38 Message-ID: References: <7cosa7$rgl$1@nnrp1.dejanews.com> <36F01E44.8DB3CAE4@swbell.net> <1doxxsz.5zmnapzv7ggaN@dempson.actrix.gen.nz> <3701FF21.C4F327BD@swbell.net> <37020A8B.46585F3E@iolinc.net> <37023162.11165D84@swbell.net> <37041CA0.6C13D2DE@iolinc.net> <3704A7A3.72AE153F@swbell.net> <3704B626.DF28564C@iolinc.net> <370C3F1C.8D3C3DA3@swbell.net> <370CB616.B63AD078@swbell.net> NNTP-Posting-Host: wraith.cs.uow.edu.au X-Trace: wyrm.its.uow.edu.au 923627584 5827 130.130.64.1 (9 Apr 1999 03:13:04 GMT) X-Complaints-To: usenet@wyrm.its.uow.edu.au NNTP-Posting-Date: 9 Apr 1999 03:13:04 GMT X-Newsreader: NN version 6.5.0 #15 (NOV) Xref: news1.icaen comp.sys.apple2:146701 Rubywand writes: >David Wilson writes ... >>The only problem with this change is that the ROMs in a ][ or ][+ are not >>pin-compatible with EPROMs of the same size. Thus, to make this change you >>would need to wire an adapter between the EPROM and the ROM socket to sort out >>the chip select polarities. > True. The 2516 and 2716 2k x 8 PROMs come close. > One problem is that the ROMs have three enable/select pins; the PROM has two. > Fortunately, the Apple II uses only two select lines; so, the main thing you >need to add to an adaptor is an inverter-- like a 74LS04 or any other inverting >gate. Acording to Jim Sather, the inverter can be dispensed with: Pin # ROM socket 2716 (except TMS2716 - use TMS2516 instead) 18 CS2 (active high) /CE (active low) 20 CS1' (active low) /G (active low) 21 CS3' (active low) Vpp (25v prog, 5v read) So if pin 18 (ROM) goes to pin 21 (EPROM) and pin 20 (ROM) goes to both pin 20 and 18 (EPROM) it should work. Looking at the 2716 data sheets I have this is not valid as Vpp is only defined at 5v and 25v, not at 0v. If you do not have any cards which drive the INHIBIT' line then this will not be a problem. >Probably, a II+ will have the Language Card plugged into Slot 0. With the LC >plugged in the $F8 ROM used is going to be the one on the LC; so, this is >where you would swap in the adaptor with the PROM. If you have a Language Card, it already has two solder points to convert it to 2716 polarity. A third point marked F8 should be left open unless you want the motherboard F8 PROM used when the motherboard BASIC is selected. -- David Wilson School of IT & CS, Uni of Wollongong, Australia david@uow.edu.au