Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!mcnc!rti!sunpix!matthew From: matthew@sunpix.UUCP ( Sun NCAA) Newsgroups: comp.sys.apple Subject: Re: Rom Copyrights Message-ID: <599@greens.UUCP> Date: 30 Apr 89 18:46:54 GMT References: <2596@ndsuvax.UUCP> Organization: Sun Microsystems, Research Triangle Park, NC Lines: 58 | I am really curious as to how one could justify copying the ][+ roms |when they appear to be of a non-standard layout. I remeber attempting |some permanent changes to the rom set (using eroms) and could never get |the ][+ to read the code that I had installed on them. The Apple ][ and Apple ][plus roms are "not really" that non-standard. Apple simply used a modified version of the 2316 rom. The 2316 rom is the chip that the 2716 Eprom was developed from. The only thing that currently inhibits the direct replacement of the Apple ][ and ][plus roms with 2716 eproms, is the polarity of one control line. The control lines on 2316/2716's are on pins 18, 20, and 21. The polarity and functions of pins 20 and 21 are the same on both the 2316 and the 2716. The polarity of pin 18 is called "active-high" on the 2316, and "active-low" on the 2716. If you look on you schematics for your Apple ][plus, you will see that the the only thing attached to pin 18 of the rom chips is a pull up resistor and the INH/ pin on slots 0 thru 7. Now if we can reverse the polarity on this line you can replace the 2316's with 2716's containing your own code. Reversing the polarity is easy to do. We are simply going to need to add an inverter to the INH/ circuit between the pull-up resistor at RA01 and pin 18 of the the rom sockets. This can be done two ways. The first is to take a currently unused circuit from on of the NAND, NOR, or inverter chips already on the motherboard. The second is to add a new NAND, NOR or inverter chip to the board (there is a kluge space in the front right corner). When I replaced the rom on my Apple ][plus, (my F0 rom failed) I used the first method. I first made the eproms I would need (after the mod, only 2716's will work in the machine (you would need to undo the mod to get the 2316's to work). Secondly I cut the trace between the pull-up resistors and the rom chips. Thirdly I cut the trace between ground and the input to the NAND gate I was going to use as an inverter (A2 - pins 12 & 13). Fourth, I ran a thread of wirewrap wire from the pull-up resistor to both of the input pins of the NAND gate (a NAND or NOR gate will all inputs tied together acts like an inverter). Fifthly I ran a wire from the output of the NAND gate (A2 - p15) to pin 18 of one of the ROM. Lastly I replaced all the ROMs with the Eproms I had made. I reassembled my machine and it worked correctly from the start. I hope filling you in on how I modified my machine will help you out. Lastly, the 2364's, 23128's and 23256's used in the Apple //e's ands Apple //c's are pin compatible with their EPROM counterparts. You will not need to modify those motherboard to do the same thing you tried on your ][plus. -- Matthew Lee Stier | Sun Microsystems --- RTP, NC 27709-3447 | "Wisconsin Escapee" uucp: { sun, mcnc!rti }!sunpix!matthew | phone: (919) 469-8300 fax: (919) 460-8355 |