replica motherboard

This motherboard has Applesoft ROMs - I've really got to get my act together!

The Integer ROM Dilema

Applesoft BASIC ROMs and the autostart Monitor that come in readily available Apple II plus systems work just fine in a rev 0 board.  One assumption with the rev 0 replica kit, is that in order to complete it, you will find an old Apple II plus for the keyboard, power suppy and case.  With the Apple II plus you also will get a set of Applesoft ROMs that can be used to populate the ROM sockets on the replica motherboard.

However all Apple ll rev 0 systems originally came with Integer ROMs and non-autostart Monitor.  Though many rev 0 systems were upgraded later on with Applesoft ROMs, you may want to operate your rev 0 system like the pioneers that purchased rev 0 Apple IIs.  In this case, you'll want to get a set of Integer ROMs and the non-autostart Monitor.   

There is a catch though.  Integer ROMs have not been available from Apple in years and the parts are not exactly pin compatible with 2716 EPROMs which are still available and could be programmed with Integer BASIC images. 

Apple Integer ROM's are identified by unique part numbers for each socket location:

341-0001-00 Integer BASIC E0
341-0002-00 Integer BASIC E8
341-0003-00 Integer BASIC F0
341-0004-00 Integer BASIC F8 - This is really the non-autostart (original) Monitor ROM
sometimes you will find a programmer's Aid ROM in D0
341-0016-00 Programmer's Aid #1

There is no ROM for D8 in a standard integer basic config

There are several approaches to setting up your rev 0 replica with Integer BASIC functionality.

Genuine Apple ROM Approach

The first and easiest method, at least in my mind, is to win an Apple ROM firmware card on ebay with Integer ROMs in it.  These boards show up periodically and the winning bid usually doesn't go over $100.  These ROM cards come with either Integer or Applesoft ROMs, but it is easy to tell them apart.  You will know that the ROM card has Integer BASIC ROMs because location D8 will rarely be populated in a standard Integer BASIC system.  Location D0 may or may not be populated in Integer systems with the Programmers Aid ROM.  Only problem with this approach is that it may take you a number of months to find and win one of these cards at a price you think is reasonable.

If you are going to buy a replica kit,  check to see if I have any Interger ROM sets available.  They are hard to come by, but occassionally I'll have a set that I will sell to replica kit purchasers at extra cost.

In addition, this site sells original Applesoft ROMs for a reasonable price.  They don't have integer ROM sets, but if you want Applesoft ROMs, they are available

Apple Firmware Card/2716 EPROM Approach

An alternative is to find an Apple Applesoft ROM card on ebay.  This is the same ROM card as mentioned above, only with Applesoft ROMs.  This card happens to have jumperable support for 2K 2716 EPROMs.  Move the Applesoft ROMs to the motherboard, jumper the 2716 connections on the ROM card,  burn some 2716s EPROMS with Integer BASIC and put them on the ROM card.  You need those Applesoft ROMs on your motherboard in order to boot DOS.

Stacking Socket Type 2716 EPROM Adaptor

Mike Fortuna has provided instructions on how to create a 2716 to ROM socket adaptor by stacking a 2716 EPROM on a socket and adding an inverter.  He is successfully using this solution to provide the "brains" for his rev 0 replica.  This is a quite clever solution, but requires excellent rework skills.

picture of 2716 solution
note the tiny inverter attached to the bottom of the 2716

Cut pin 21 on EEPROM so it will not contact socket (just above were it narrows)
Cut pin 18 on EEPROM so it will not contact socket (just above were it narrows)

Place EEPROM into 24 pin socket.

Deadbug NC7S04 SOT23 on bottom of EEPROM such that it fits inside the 24 pin socket cavity.

Attach SOT23 pin 2 to pin 18 of the socket.
Attach SOT23 pin 3 to pin 12 of the socket.
Attach SOT23 pin 4 to pin 18 of the EEPROM.
Attach SOT23 pin 5 to pin 24 of the socket.
Attach SOT23 pin 5 to pin 21 of the EEPROM.

Note the last 2 steps can be one wire from socket pin 24 to SOT23 pin 5 to EEPROM pin 21

Custom 27128/27256 EPROM Based Hardware

Finally, I designed a functional replacement ROM firmware board that accepts a single 27128 or 27256.  This board will boot DOS without ROMs on the motherboard because of some extra features that I added to it.  The single EPROM solution is about 3 or 4 times cheaper to build than a board with a bank of 2716 sockets.  This page on my website has details on that design.   I'll provide artwork, if you want to build one of these boards, yourself.  If enough intereset is generated, I might make a run of these cards.  The estimated cost of a kit would be about $40.  However, I doubt that that the interest would be enough to justify a run of cards, primarily due to availability of authentic Integer BASIC ROMs on Apple ROM cards for less than $100 on ebay.

NEW! - I now have a production version of the firmware board available.  It is called the "Brain Board".  See my "Brain Board" web page for details.

Bill Garber has designed a 27256 EPROM replacement daughterboard that fits right on the Apple Motherboard in place of ROMs. (seem like a dead link)

Stacking Socket Solutions that Don't ReallyWork!

The following socket stacking solutions do not properly support the Apple II's inhibit function which means that firmware and language cards will not work with this solution.   See Mike Fortuna's solution for what should have been done.

As mentioned before, 2716 EPROMs are not pin compatible with the Apple supplied ROMs.  However you can stack a couple of sockets and reroute a few wires between the sockets in order to support 2716s.  One example is described in the book, "Understanding the Apple II" and online here.

This site has these adaptors built up and for sale.  They apparently will also burn EPROMs with images for you, if you provide the images.

To save you time, they have pre-burnt EPROMs with images for each Apple ROM here.

Sources for Rom Images

Folks who have written virtual emulators of the Apple II have hints for finding ROM images on their sites. In any case, Apple owns the copyright to this code, so I can't freely reproduce them for you.  If you have a set of Integer ROMs, you can easily dump them using Apple's monitor from an Apple to a serial port.

An EPROM Programmer

One other item should be mentioned in regards to the 2716 or 27128 solutions.  EPROM programmers are very inexpensive these days.  Find a Willems type programmer that works off of a PC's parallel port.  I bought mine off of ebay for around $19.00 and it works just fine. 

Replica PCB with 2716 EPROM Support?

I did consider altering the rev0 layout to support 2716 EPROMs.  However the motherboard would not then have an authentic layout and there doesn't seem to be enough interest in this expensive kit to justify a non-authentic variant. 

Back to Mike's Hobby Home Page