ULA ZX8301 - TV Picture Capabilities

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tcat
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ULA ZX8301 - TV Picture Capabilities

Postby tcat » Sat Jan 14, 2017 8:42 am

Hi,

Inspired by an excellent interview of Urs Koening with David Karlin, I am thinking of adding more colours to standard QLs. It seems a single pin was eliminated in the process of cost cutting before QL mass market production.

http://www.sinclairql.net/story/The_lon ... Karlin.htm
Q: Why has a non-common FLASH option been implemented and not a more desirable and usable 16 colour option (BRIGHT of the 8 base colours or real 16 colours)? Was this because of Teletext/BBS/Videotex/MicroNet/Prestel or the like had flashing characters?

DK: I hardly remember this. The ZX8301 is purely digital, so to get multiple colour levels, we would have needed an extra output which would have fed a primitive DAC. This would have needed another pin, and we didn't have one.


Question, is `ULA ZX8301' in fact capable of more colours so just by supplying some simple logic we could trigger 16 true colours with BRIGHT shading like on ZX?


Cheers
Tomas


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tofro
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Re: ULA ZX8301 - TV Picture Capabilities

Postby tofro » Sat Jan 14, 2017 10:42 am

Tomas,

Nice idea. I think 8 more colours would be much more useful than FLASH.

the question of whether the 8301 would support or not support more colours is kind of academical. Even if it were, you might probably be having some problems adding that missing pin (rather "bit") of color :)

What could be done, however, is replacing the 8301 with a replacement, functionally (nearly) equivalent chip, based on programmable logic (i.e. CPLD or FPGA). The video generation circuit would be pretty straightforward and would use the 4th bit in a colour as a "BRIGHT" bit towards the video circuit instead of the dreaded FLASH (That would be the "missing pin" the interview relates to. The video mixing circuit would also need to be expanded, in order to mix this BRIGHT signal with the R, G, and B signals - Something that could be copied from the Spectrum.

Apart from video generation, the 8301 does some address decoding for the 8302 and the ROM slot, the CPU clock divider and also needs to supply the DTACKL signal to the expansion bus, and, most importantly, DRAM refresh. These functions would obviously also need some re-engineering.

The 8301 functions are pretty well documented in the QL service manual.

Cheers,
Tobias


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Re: ULA ZX8301 - TV Picture Capabilities

Postby Derek_Stewart » Sat Jan 14, 2017 11:14 am

Hi,

Spectrum ULA replacement: mULA48, uses a Xilinx CPLD XC95144XL

Could this be done on the 8301, which could give the flexibility for extra colours.


Regards,

Derek
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Cristian
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Re: ULA ZX8301 - TV Picture Capabilities

Postby Cristian » Sat Jan 14, 2017 1:00 pm

tofro wrote:I think 8 more colours would be much more useful than FLASH.

:lol: :lol:
Now seriously: QL resolution + more colors = rocking revolution :o


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Re: ULA ZX8301 - TV Picture Capabilities

Postby tcat » Sat Jan 14, 2017 2:14 pm

Nice idea. I think 8 more colours would be much more useful than FLASH.


Hi All,

Perhaps not that nice idea after all.

I was hoping to discover something really simple me capable of, as ZX8301 seems true heart of QL with nice ideas, minimising number of components used. Its replacement would probably kill the QL spirit. If there were a possible extension of one missing pin/bit in lieu of FLASH to wire, to double number of colours, feeding right into PAL chip at least I hope there is one doing RGB signaling to the monitor. Also important to keep compatibility to all QL s/w mostly distributed on carts.

Tomas


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Re: ULA ZX8301 - TV Picture Capabilities

Postby tofro » Sun Jan 15, 2017 11:33 am

Ralf R. wrote:How does it work in the Thor 16?


The Thor XVI doesn't use the QL custom chips. Its video generation circuitry is entirely different from the QL. From the information I have, I suppose it entirely uses discrete logic. It does support both the usage of the 4th bit as flash (MODE 8) and BRIGHT (MODE12 - unclear to me BTW why it was named that way) bit. Note for the 16-color mode to work on the Thor XVI, the monitor must support an extra intensity input. Not all do.

Tobias


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Re: ULA ZX8301 - TV Picture Capabilities

Postby Derek_Stewart » Sun Jan 15, 2017 12:53 pm

Hi,

Do you think it is possible to read the 8301 code and disassemble it, lke Laurence Reeves did on the 8049.

I am not sure what sort of device the 8301 is.


Regards,

Derek
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Re: ULA ZX8301 - TV Picture Capabilities

Postby tofro » Sun Jan 15, 2017 1:41 pm

Derek,

there's no code in a 8301 - only transistors.

The 8301 is an ASIC or a gate array - A chip that has a lot of pre-fabricated, non-connected, NANDs and NORs on the wafer. During the last stages of the production process, the "wires" are being added between the gates making up the final circuit. That would rather compare to wire-wrapping than to programming. Programmable hardware was only developed as late as in the early nineties.

The only way to get out the wiring diagram would be to use a good microscope...

But fortunately, we pretty well know what the chip is doing and could be mimicking this behaviour in a HDL.

Tobias


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Re: ULA ZX8301 - TV Picture Capabilities

Postby Derek_Stewart » Mon Jan 16, 2017 8:59 am

Hi Tobias,

I forgot about the 8301 being a Gate Array, this should make the process easier.

I always though that the QL Second Screen area could be utilised as extra screen resolution. Maybe an enhanced Gate Array to access the extra screen memory.


Regards,

Derek

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