What is a Quadlink? It's an ISA expansion card from the '80s designed to turn your IBM PC (such as a 5150 or 5160) into an Apple ][! After booting and running the software, you can switch quickly between PC and Apple mode using Ctrl-Alt-A (for Apple) and Ctrl-Alt-P (for PC).
I'm not selling this board, but the complete design files are available here so you can build it yourself. As an alternative, a2heaven sells a kit with the PCB and all the components. (I have not personally built one of these kits.)
All of the components are readily available. In the bill of materials, Mouser part numbers are listed where available. The RAM chips, 27C32 ROM chip, and NE558 may be obtained from a variety of sources in China, but they are not guaranteed to work, so I recommend getting 1 or 2 extras just in case. Note: It has been reported that a Signetics NE558 with a date code of 8825VI, commonly available from China, does not actually work. If you can't find any working 558 chips, try building my replacement that uses four 555 chips.
Please note that the 0.1" header pins are not listed on the BOM. They are standard breakaway headers.
The memory chips (4416 and 4164 RAM) are both 150ns types.
This board is a straight forward 2-layer board. Ideally you should specify selective gold plating (hard gold) for the edge fingers, but this gets very expensive for small orders. ENIG will work but the gold will rub off fairly quickly.
Board dimensions are 13.335" x 4.24" (338.7mm x 107.7mm).
For the soldermask color, pick whatever you want!
I recommend using sockets for the memory chips, CPU, and all the PALS. You'll also need a socket for the joystick/paddle connector. The list of sockets required is as follows:
| Quantity | Position | Type |
|---|---|---|
| 9 | U1-U4, U20-U23, J4 | 16-pin, 0.3" wide |
| 2 | U5, U24 | 18-pin, 0.3" wide |
| 1 | U11 | 24-pin, 0.6" wide |
| 1 | U48 | 40-pin, 0.6" wide |
| 10 | U7, U8, U27, U30, U33, U34, U40, U49, U50, U51 | 20-pin, 0.3" wide |
If you plan to install the card in an IBM 5150 or 5160, you'll plug the floppy drive cable (the one going between the existing controller and the floppy drives in your computer) into the P2 edge connector on the card. Solder a shrouded header at the J7 position with the keying notch pointing downwards. Later on, you'll make a short cable to go between the floppy controller card and J7.
If you want to use the card in another system (note: I have not tested this yet!) with a standard IDC header instead of an edge card connector, solder unshrouded headers at both the J7 and P3 position. Your existing floppy cable will plug into P3, and you will need to make a short cable that connects J7 and your existing floppy controller card.
J5 and J6 are right-angle 0.1" headers. You can use a single 8-pin strip. Remember to pull pin 2 on both header positions since this is the key for the cable that plugs in. This is also marked on the back of the PC board.
If you are using an NMOS 6502, you can connect the solder jumper on the back of the board right next to the chip. CMOS 6502 chips repurpose this pin and the solder jumper should be left open.
Note for European users: it might be tempting to configure the solder jumpers on the back of the card for PAL timings rather than NTSC, but I have not tested this configuration. The original Quadlink has solder paste covering the jumpers, implying that they never fully tested it. Use it at your own risk.
I've created a CAD model of the original Quadlink bracket. If you have access to sheet metal tools (or even just a chassis nibbler) then you can reproduce it. Once it is in the right shape, bend the top using a press brake or even just a bench vise. The material is 0.035" (0.9mm) steel, brushed and painted black.
There are 11 programmable devices on the Quapple. One of them is a 27C32 EPROM which contains the character set for the text mode. I didn't have much luck using the Minipro TL866 device to program my Intel 2732 devices, so you might have to try a few to find one that works. You might also try using a flash device (28C32?) instead, but I have not tested this myself.
The remaining programmable devices are all PALs. You can use an ATF16V8 (speed grade is unimportant here), which happens to be supported by the Minipro TL866.
Use the JEDEC files (.jed) with the following Minipro command line under Linux:
minipro -p "ATF16V8B" -w [file.jed] -P
The full, commented, PAL source code is provided for educational purposes. If you want to modify them, you can use WinCUPL to build them.
I recommend marking the PALs with colored dots, labels, or permanent marker so you don't mix them up and put them in the wrong sockets.
PAL functions are as follows:
| Position | Function |
|---|---|
| U8 | Video address decoding (simple) |
| U27 | Video address decoding (complex). Video sync. |
| U7 | Clock generation |
| U30 | Soft switches |
| U33 | Color attribute generation |
| U34 | ISA bus address decoder |
| U40 | Disk controller |
| U49 | 6502 state machine |
| U50 | More soft switches |
| U51 | RAM/ROM mapping, CAS control, RESET inverter |
You will also need to build several cable assemblies to connect the Quapple to your PC.
For use with an IBM 5150 or 5160, make a short, 6" (15cm) IDC ribbon cable, 34 pin, with a 0.1" female header at one end and a 34-pin female edge connector at the other end.
For any other computer, just crimp a 34-pin 0.1" female header at both ends. Be sure not to get pin 1 mixed up--it is very easy to do!
To use the same monitor for both Apple and PC mode, you'll need a short cable to go between the Quapple and your regular video card (MDA or CGA). This is just a short cable with a male DE-9 connector at both ends, wired straight through (pin 1 to pin 1, etc).
The stock cable is 12" (30.5cm) long and uses a TE Connectivity/AMP 745032-1 connector, along with a cord guard, 207753-1, at both ends. The contact part number is 1-66506-0. The cable is 0.24" (6mm) diameter with eight conductors (the drain wire is connected to pin 1).
To hear Apple sound through the PC speaker, make a short 2-wire cable (maybe 2-3" long, depending on your computer). This goes from the motherboard to the Quapple.
The cable should be wired as follows:
- Pin 1 connects to pin 1 (black wire)
- Pin 2 is a key (plastic peg inserted in the opening) at both ends
- Pin 3 is not used
- Pin 4 to pin 4 (yellow wire)
You'll want to install the card in the second-to-last slot (5150) or third-from-last slot (5160). This is because the floppy controller should be in between the Quapple and the power supply, just to make cable routing easier.
Before you start, plug the short floppy jumper cable into J7 on the Quapple. Also plug the 4-pin PC speaker jumper cable into header J6.
Remove the floppy controller and disconnect the drive cable from it. Plug the drive cable into the Quapple connector P2 (or P3, if the cable has a 0.1" socket at the end). Unplug the PC speaker from the motherboard.
Then plug the Quapple into the PC slot, managing the floppy cable as needed. The 4-pin jumper should plug into the motherboard's PC speaker header, and the PC speaker cable should plug into J5.
Then plug the short floppy jumper cable into the header on the floppy controller, and plug the floppy controller back into an adjacent slot. Since the card is shorter, it's much easier to use the slot that is closer to the power supply.
Finally, connect the DE-9 jumper cable between the video card and the lower connector on the Quapple. This step is optional since you can use the card with a dual monitor configuration, or even with the composite video output jack.
You can find the software at the link below, along with the manual of the original Quadlink. There are three disk images you will need: the Quadlink System Master, the Quadlink Filer, and DOS (I used PC DOS 1.10, but feel free to experiment). The Quadlink System Master disk has an executable, QUADLINK.EXE, which should be copied to the DOS disk.
The Filer disk can be written using a flux imaging tool, or possibly with an Apple II running ADTPro.
A note about compatibility: I have only tested the card in an IBM 5150. It's supposed to work in a 5160 as well. Based on looking at the design, I see no reason why it wouldn't work in a faster machine, but there may be CPU-dependent hardware loops in the Quadlink executable that would prevent it from working.
Once you have the disks, insert the DOS disk and turn on the computer. After it boots, run QUADLINK.EXE and follow the prompts. When you insert the Filer disk, the software copies the entire Applesoft ROM from the disk into a special 16K memory on the card and write-protects it. Hit a key to get back to DOS, and then press CTRL-ALT-A. If you see the Quadlink banner, hit CTRL-ALT-DEL to boot the Apple.
This can be a tricky card to troubleshoot. The QUADLINK.EXE doesn't really provide good error diagnostics, but if you can get it to access the Filer disk, then you know that the 6502 is running code and trying to copy data from the disk.
Someday, when I get a chance, I'll look into writing a diagnostic program to help with the process...
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