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Correct baud rate generator chip for Kaypro II

D

DavidWien

Experienced Member
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Apr 30, 2026
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Vienna, Austria
My Kaypro II-83 had a non functioning U78 Baud Rate Generato chip, WD8116M-00. Does anyone know the difference between this and WD8119-PD, which is what I have tried. The result is wrong characters on the screen. I will try to get hold of the original chip, but they seem very thin on the ground.

I am looking for a WD8116M-00, but so far have had not found one. Can anybody help?

Thanks!

David
 
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The WD8116 is supposed to be same as WD1943.

Photo attached from EBAY.


Larry
 

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ldkraemer said:
The WD8116 is supposed to be same as WD1943.

Photo attached from EBAY.


Larry
Click to expand...
The problem is that there are variations of them for different crystals and UART dividers (16X, 32X, ...). Those photos are for a "-06" variation, which is not the "standard" part and not what is required by the Kaypro.
 
durgadas311 said:
The problem is that there are variations of them for different crystals and UART dividers (16X, 32X, ...). Those photos are for a "-06" variation, which is not the "standard" part and not what is required by the Kaypro.
Click to expand...
Not only is it "not required", it doesnt work! I am hoping that an AY-5-8116 will work. Can anyone confirm that it is an acceptable replacement for the WD chip?
 
From my quick assessment an AY-5-8116T (with NO dash extension) should work.

I used the Kaypro II schematics to find that U78 was identified as a 8116 with a 5.0688 MHz crystal.

The datasheet for the AY-5-8116 identified that the pinout corresponded to that on the Kaypro II schematic.

In particular that pin 10 is not used. This is a subtle difference between the 8116 and the 8136.

The datasheet indicates two (2) different tables - one for a 5.0688 MHz crystal and the other for a 4.9152 MHz crystal. The difference in the part number being that the latter is a -005.

I suspect that the 8116 came in different 'dash number' flavours to suite various applications. You need to purchase a 8116 part without a dash number to work with the specific crystal within the Kaypro II.

Hope this is of some help to you in your quest.



EDIT: Just checked the Kaypro II schematic and datasheet pinout a bit more closely and they agree pin for pin. Just check (with a multimeter) between pin 2 (+5V) and pin 11 (0V/GND) to make sure that the power pins are where we think they should be...

Dave
 
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It is not just a question of agreement in pin labelling on the datsheets. Pin 10 is not connected in the Kaypro, so that doesnt matter, apparently. But the internal workings do matter, and differ according to the suffices. The original part for the Kaypro II is WD8116M-00 (the one with the red dot in this photo): the one above it does not work in my Kaypro, though it possibly might if the crystal frequency were different.

wm8116-comparison.jpg

David
 
This is why I also looked at the crystal frequency for the AY-5-8116.

If you have an oscilloscope or frequency counter you should be able to look at the frequency output to the UART to see if there is anything present when you used a replacement.

Looking at the pinout of the device verses the schematic is the first step. Any anomalies here render any potential replacement device unusable.

Likewise, double-checking the power rails of the actual device is important to prevent any damage by using a replacement - especially if the schematic is wrong (either accidentally or on purpose).

If you can find the datasheets for both the original and the proposed replacement you are in luck. if not, you have to make your best guess...

Without the datasheets you have to do the best you can under the circumstances.

Dave
 
daver2 said:
This is why I also looked at the crystal frequency for the AY-5-8116.

If you have an oscilloscope or frequency counter you should be able to look at the frequency output to the UART to see if there is anything present when you used a replacement.

Looking at the pinout of the device verses the schematic is the first step. Any anomalies here render any potential replacement device unusable.

Likewise, double-checking the power rails of the actual device is important to prevent any damage by using a replacement - especially if the schematic is wrong (either accidentally or on purpose).

If you can find the datasheets for both the original and the proposed replacement you are in luck. if not, you have to make your best guess...

Without the datasheets you have to do the best you can under the circumstances.

Dave
Click to expand...
This has been done. The Kaypro programs the port in question using code 05H to select 300 baud, normally producing 4800Hz (Z80-SIO is programmed for 16X). These suspect parts, when put in the Kaypro, produce about 6400Hz which matches the WD8116-06 characteristics (part is intended for 32X) if used in a Kaypro (programmed with 05H on a 5.0688MHz crystal). Note that the -06 has different encoding than the -00, where 05H means 200 baud instead of 300. That's in addition to the 32X vs 16X.
 
One point of confusion here was the apparent change in how WD labels their parts. These parts from the early 1980's are labeled "WD8116M-00 / WD1943M-00" while these parts on ebay from the late 1980s are labeled "WD8116-PD / WD1943-PD / 06-02" ("-PD" means "Plastic, DIP") making it less obvious that they are "-06" as referenced in the datasheet. Since the datasheets are pages extracted from a larger databook/catalogue, we'd have to find that book and look for a section on packaging/ordering. But we'd need one from the late 1980s.
 
The long-awaited AY-8116 chip arrived from Poland at lunch time and here is the result of swapping it for the
WD8116-PD:
L1010545_b.jpg

So, we got to first base. Many thanks to those who helped and encouraged me from the sidelines!

I am going to screw the top on for a while, as I refresh my memory of CP/M commands and put the Kaypro through its paces. But I shall be back...

David
 
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