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Last revision of this page: November 7, 2024

There are two variants of the MICROCode KayPLUS ROM. The -83 (versions 0.1c & 0.1e) and the -84 (version 1.2a) variant. The designations are actually self-explanatory. The -83 variant is intended for the 81-110 and 81-240 mainboards, the -84 variant for all others. I was quite happy when I found the -83 variant with the file name version v0.2a in a ZIP file. But unfortunately it turned out (hex viewer & MD5 checksum) that this was only version 0.1c. Too bad.

In principle, the -83 version can also be used in the Kaypro 10('83); 81-180 PCB number. These first ones were delivered with different intermediate boards (81-212). There are: 81-212, 81-212 mod and 81-212A. I use the 81-212A version and the KayPLUS-83 does not seem to work with this version. Read below.

Note: All KayPLUS ROM's (-83 and -84) are 8K of size!

The knowledgeable Kaypro user should now be little perplexed. How am I supposed to use a Kaypro II or IV with 81-110 or 81-240 mainboards? There is room for 2K (original) or 4K, but certainly not for 8K! Only the later Universal Boards have 8k ROMs.

Features

Monitor

The KayPLUS ROM has a minimalistic monitor. No other Kaypro ROM that I know of has this feature, not even the various ROMs from Micro Cornucopia. Just press ESC when the boot message appears and jump into the monitor.

And now you have the option of starting from a floppy disk drive (from A or B). This can be a 5.25" or 3.5" floppy drive!

See manuals below.

As mentioned above, the Kaypro II only has one ROM socket for a 2K EPROM. This can easily be modified to 4K (2716 to 2732). Turning a II into a 4.

And then there is a very special 8K mod for the 81-110A board for the Kaypro II. Do not be confused by the CHARROM label (CD32). This is a normal 81-146 ROM. This board was a bargain on eBay US.

The mainboard has the serial number #1797. But even if you can't directly deduce the serial number of the corresponding Kaypro/Kaycomp II from this serial number, this board is one of the very first! I own a Kaypro II with the serial number #4037, which has an 81-110A PCB with the serial number #2035 installed.

What did you do in July 1982? It was my summer holidays and I got my sailing licence (inland A) on the Maschsee in Hanover.

If you want a better ROM for your Kaypro 10 (83 or 84), then MICROCode's KayPLUS might be right for you. Basically it works in my Kaypro 10/83, but ...

It depends on what your original ROM is on the motherboard. If it is the 81-188, then you have a good chance, if it is the 81-302C or 81-277A, then there will probably be problems with the hard drive. I have the 81-277A ROM and the KayPLUS-83 works fine with the floppy drive, but the hard drive cannot be accessed. My research on the internet has shown that this is due to the intermediate board (81-212x) between the motherboard and the hard drive controller.

Kaypro did go through a lot of revisions of their systems. I also found some issues with the KayPLUS ROM documentation. As to the K10, if the model number of the main PCB is 81-180 B or C or whatever with an 81-302 ROM then it is definitely an 83 model K10. If it's anything else then it's most likely an 84 model K10. I have an 83 model K10 and it has a small interface board between the main PCB and the WD1002 controller. It's kind of over kill for just two IC's. It has the decoder for the WD1002 and a 74LS00 that inverts the reset line and I think the read and write lines.
This is where the documentation for the KayPLUS ROM is just plain wrong. In section J at the top of page 30 it states that the level of the reset line from the main PCB is LOW to reset the WD1002 on the 83 model K10. WRONG! The level of the signal coming out of U11 pin-19 is HIGH to reset and then goes LOW a short time after boot up. The WD1002 controller requires a LOW level reset signal, which is why there is an inverter on the interface board. The KayPLUS ROM leaves this signal HIGH all the time, which keeps the WD1002 controller in reset. I might add that the schematic for the 83 model K10 has the signal label incorrectly. It show's J9 pin-45 as a LOW active reset signal when in fact it is a HIGH active signal.
Since the KayPLUS ROM doesn't make use of the reset signal on pin-45 I chose to modify the interface board between the main board and the WD1002. Pin-43 of J9 has the LOW active system reset signal. I cut the trace on the interface board that comes from pin-45. There is an unused section of the 74LS00. One of the input pins is wired to ground so I removed the ground and then removed the 74LS00 and replaced it with a 74LS132 quad nand Schmidt trigger IC. Now I added a wire from pin-43 to the two input pins of the spare nand gate and then wire the output of this gate to the old input on the nand gate that came from pin-45. I put everything back together and guess what, I can now talk to the hard drive. [1]

Hi All,
To get down to specifics as pointed out on page 30 of the KayPLUS documentation, there were two types of interface cards used in the K10. Systems with the old interface used a LOW active reset signal while the new boards used a HIGH active reset signal. If your K10 has an 81-188 ROM then you have the early version of the interface in your K10. The KayPLUS ROM will work just fine in these systems as the ROM monitor leaves this bit HIGH, removing the LOW active reset signal to the interface card. If you have a system with the 81-302 ROM then the KayPLUS ROM will NOT work because these systems use a HIGH active reset signal to the interface card. The newer interface card has an inverter in the reset line that sends a LOW active reset signal to the WD1002 controller. The KayPLUS ROM leaves the reset line HIGH and that causes the WD1002 controller board to stay in reset.
The top paragraph on page in the KayPLUS documentation contradicts the instructions in section M. It says to use the KayPLUS-84 ROM in ALL K10 system. This ROM will only work correctly if you have the early version of the interface board. To use the ROM on the later version of the interface card then you need to remove the inverter on the interface card. The hard drive will then work just fine. If you want to add a second floppy drive, as I did, to your K10 then a whole different approach to the reset signal is needed.[1]

• KayPLUS-83 (Kaypro II, 2-83, 4-83)
• KayPLUS-84 (Kaypro 10, 2-84, 4-84)

1. (↑) Don Maslin at https://groups.google.com/g/comp.os.cpm/c/IRXsnekNgSg/m/VZQdbytIPBYJ

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--> Go to Part 7 : Terminal
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