ZON X-81 vs ZON X

Discussions about Sinclair ZX80 and ZX81 Hardware
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ZON X-81 vs ZON X

Post by kpalser » Sun May 13, 2018 10:28 pm

Hi AY Gurus,

I’m planning to add ZON support to my emulator. Looking at resources like:
https://k1.spdns.de/Vintage/Sinclair/80 ... %20Module/
https://k1.spdns.de/Vintage/Sinclair/82 ... %20Module/

and then the source code for EightyOne and SZ81 it’s clear which port addresses to use in OUT code to create generic ZON emulation with respect to setting the AY register and writing data to the AY.

I want a different scenario where I can offer BI-PAK settings:
1) Generic like the above
2) ZON X-81
3) ZON X (the successor)

I.e. I want programs to fail if they are not compatible with the selected model (2 & 3 above).

The understanding is that the addresses changed for ZON X to be compatible with the Spectrum. The links I have consulted and the source code comments indicate that there were inaccuracies in the BI-PAK manuals. I've been trying to buy real ZONs but they are not easy to find after all these years.

So can any of you confirm the select register and write register addresses based on REAL device tests for both models?

Searching this forum for "ZON" is not easy when the words need to have 4 or more characters. However, I see in viewtopic.php?t=861 - Would "ZON-X81-Clone" also cover "ZON X" cases?


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Re: ZON X-81 vs ZON X

Post by Dim_75 » Tue Feb 05, 2019 1:00 am

Hello Kpalser,

I don't find many things in my archives but does this schematic is of any help in your research ?
It shows some differences between ZON x-81 and Zon-X boards.

ZON ZX81 schematic.jpg

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Re: ZON X-81 vs ZON X

Post by kpalser » Wed Feb 13, 2019 8:51 pm

Hi Dim,

After you kindly responded in the ZX81 Owners Facebook group I started looking at the notes on the schematic and with the help of Sirmorris testing using his real ZON X-81 the following conclusions were reached for the port addresses:

A0 to A3 are always high
A4 can be low or high for ZON X-81 but has to be high for ZON X
A5 & A6 are not used in the decoding
A7 is low to write to register and high to latch a register

Latch register

8F, 9F, AF, BF, CF, DF, EF, FF = ZON X-81 (verified)
9F, BF, DF, FF = ZON X

Write data

0F, 1F, 2F, 3F, 4F, 5F, 6F, 7F = ZON X-81 (verified)
1F, 3F, 5F, 7F = ZON X

Thoughts on the above:
- A lot more possible port addresses than the documentation and many emulators would cover.
- As https://k1.spdns.de/Vintage/Sinclair/82 ... %20Module/ reports it looks like the documentation on the “ZON X” has the wrong write data port on the last page of the manual.

We should verify this on real hardware - due to the ZON X documentation:
The popular AY Demo would not produce sound on a “ZON X” but it does work on a “ZON X-81”.

;entry: b=AY reg, c=reg data
;exit:  a corrupt
;XXX currently Zon X-specific
ld a,b
out (0dfh),a
ld a,c
out (0fh),a
(14.03 KiB) Downloaded 50 times
For the purpose of hex editing the Y demo P file:
DF port value is at byte location 759 (decimal)
0F port value is at byte location 762 (decimal)

So does anyone have the “ZON X” model and a ZX81 with a 16K RAM pack to hand to verify the above?


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