Sparkly pixels

Discussions about Sinclair ZX80 and ZX81 Hardware
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1024MAK
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Re: Sparkly pixels

Post by 1024MAK »

Using ZX81 2C184E and 2C210E ULAs as an example, These are most likely Ferranti ULA 2000 series very high speed CML (Current-Mode Logic cell) types, that have the following specs: max. clock speed 20MHz, gate delay 8ns, gate current 210µA, matrix size 15 x 15 x 1, total matrix cells 225, total peripheral cells 40.

The CML type has a Vcc to suit the logic it is interfacing to (3.5V to 5.5V). The peripheral cells run directly from this supply. The CML matrix cells use a 0.95V supply and are fed via on chip series voltage regulators. If required, the regulators can have their own supply pin (Vreg), in which case the input supply voltage can be between 1.3V and Vcc to minimise power dissipation without compromising speed. Otherwise (like in the Sinclair ZX81 design) both are fed via the same power pin (the ZX81 ULA only has a single positive power supply pin).

As well as the regulator circuitry, a large power consumer is the peripheral cells.

To construct a logic gate, one or more CML matrix cells are needed:
Buffer =1 cell
2 input NAND gate = 1 cell
3 input NOR gate = 1 cell
monostable = 2 cells
data latch = 3 cells
binary divider with preset and clear = 3 cells
D-type flip-flop with preset and clear = 6 cells

Mark
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ZX81 Video Transistor Buffer Amp

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Moggy
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Re: Sparkly pixels

Post by Moggy »

Great info there Mark and explained in a way even I can understand! :lol:
Lardo Boffin
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Re: Sparkly pixels

Post by Lardo Boffin »

I'm not sure what is sparklier - my pixels or the debate they have caused! :lol:
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ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
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PokeMon
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Re: Sparkly pixels

Post by PokeMon »

Moggy wrote: The ONLY point I am trying to get across is that in an enclosed unventilated system heat sinks serve little purpose without a through put of air like a PC for example.
I totally agree with you. This is plain physics of thermodynamic laws which in general states, that energy can be converted only but not eliminated (even not partly). So in basic words the energy of the ULA is used to heat the air inside the case and of course the case itself. Putting a heatsink in a closed system with no air ventilation doesn't harm the system at all.

Lets see the DIP 40 package with typical tj-a (junction ambient) of 76 K/W and tj-c (junction-case) of 19 K/W. Then you add a heat sink with lets say typical 18 K/W. You would think you have now 37 K/W which is better than 76 K/W. Yes and no. In an open system with air convection yes, in a closed system no. Why no ? The heatsink is able to heat the air inside better (and hotter) than the plain dip ic. There would be an effect for a short period but for longer periods there is no change as the heatsink can not "burn" energy. It can give it faster to the air. If the air doesn't change the air is just faster or better heatened.

Here is a nice graphic on air-flow effects and influence on thermal resistance:
Bildschirmfoto 2017-01-21 um 23.12.16.png
Bildschirmfoto 2017-01-21 um 23.12.16.png (106.75 KiB) Viewed 4121 times
Read more stuff about ICs and airflow here:
http://www.bitsonchips.com/references/ref42.pdf
Moggy
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Re: Sparkly pixels

Post by Moggy »

@ lardo.
Feel free to start more debates Lardo I've really learned something from this one thanks to Mark and Karl and one of the nice things about this forum is that flame wars don't erupt no matter how passionate the discussion. :D

@Pokemon

Thanks Karl some really useful info there. :D
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1024MAK
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Re: Sparkly pixels

Post by 1024MAK »

Moggy wrote:@ lardo.
Feel free to start more debates Lardo I've really learned something from this one thanks to Mark and Karl and one of the nice things about this forum is that flame wars don't erupt no matter how passionate the discussion. :D

@Pokemon

Thanks Karl some really useful info there. :D
No, no, NO!
We are not all supposed to end up agreeing :lol:

Right, carry on as you are... :D

So instead of a heatsink, you need a small micro-fan :lol:

But changing the 7805 for a RECOM or similar switching regulator, or using a regulated 7.5V to 9V external power supply (* see note) is the better solution. A switching regulator produces hardly any heat. While a 7805 run with a lower input voltage of 7.5V will only dissipate half the amount of heat compared to when using a Sinclair PSU.

* Note that some third party 16k RAM packs will not work with a lower external supply, as they take advantage of the Sinclair non-regulated supply being around 10.8V to 12V, to form a "12V" supply for the 4116 DRAM chips.
You also have to be careful when using any expansion when using a switching regulator, in case the voltage of the Sinclair PSU is now too high... As when using the switching regulator, the output from the Sinclair PSU will be higher than if using a 7805.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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PokeMon
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Re: Sparkly pixels

Post by PokeMon »

1024MAK wrote: So instead of a heatsink, you need a small micro-fan :lol:
I will think of extender boards with included fan to attach on the backside. :mrgreen:
Or a "fridge" case.

Due to construction inside the box and small outlets there is not much air flow. There is a smaller cutout for the edge connector to exchange air. Unfortunately this is available only when playing with a 1k Zeddy and LOAD/SAVE via audio files only. As soon as you connect anything to the ZX81 (even a small ram pack) the hole on the backside is completely filled with an edge connector and there is nearly no more ventilation possible.

Yes - changing the voltage regulator is recommended I would say. Especially when attaching external boards like ZXpand or similar. It should take heat from inside and due to this effect "cool" the ULA. At least a little bit, few degrees. And without any heatsink.
Moggy
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Re: Sparkly pixels

Post by Moggy »

Apparently Uncle Clive asked various manufactures to come up with a cooling solution for the ULA it would seem this was the minimum needed.
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Lardo Boffin
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Re: Sparkly pixels

Post by Lardo Boffin »

Moggy wrote:@ lardo.
Feel free to start more debates Lardo I've really learned something from this one thanks to Mark and Karl and one of the nice things about this forum is that flame wars don't erupt no matter how passionate the discussion. :D

@Pokemon

Thanks Karl some really useful info there. :D
My next question is 'which pet is better? A cat or a dog?' *

On a serious note however it is really interesting how these simple questions (why do I have sparkly pixels?) evolve so much!

What never ceases to amaze me is how much people on these forums know! I often wonder what people do for a living / hobby to know so much. On the Beeb forum I asked a question about procedural error handling in BASIC (http://stardot.org.uk/forums/viewtopic.php?f=2&t=11973) and somebody produced a software fix for the error handling that even the original designers of the machine didn't include!

If you want someone who can mentally align the business processes of a Computerise Maintenance Management Software package in an engineering department with a large scale ERP such as SAP and produce a message passing interface to allow them to communicate effectively and move forward the engineering department business needs I'm your man! I'm not saying I made the best use of my engineering degree but it's indoor work with no heavy lifting and to be honest generally an interesting challenge but it's not exactly a hard core engineering job. What little I learned about this stuff in O level physics and my degree has long since gone! :?: Much respect to those that know and understand this stuff. And of course thanks for sharing!

Sadly I have a busy week ahead and so will not be able to solder my replacement regulator in for a while and therefore won't know if this fixes my issue.

* It is of course a cat.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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RetroTechie
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Re: Sparkly pixels

Post by RetroTechie »

@Moggy: you're looking at the wrong end.. that's not a cooling solution, but a HEATING solution! :lol:
Moggy wrote:The ONLY point I am trying to get across is that in an enclosed unventilated system heat sinks serve little purpose without a through put of air like a PC for example.
Still it's useful. Thermals are calculated as a set of thermal resistances in series. Semiconductor die -> case, case -> IC cooler, cooler -> ambient air. The thermal resistances are added up (Kelvin/W), then multiplied with the chip's dissipation (W), result is the ambient air <-> IC die temperature difference. Plastic case -> ambient air has a higher thermal resistance than plastic case + metal slab -> ambient air. Even if you take for "ambient" the inside of a ZX81 filled with warm air.

That said: even with a cooling plate on top, there's still a layer of -relatively poor heat conducting- plastic between IC die and cooling plate. So there's only so much a cooler can do.
1024MAK wrote:The CML type has a Vcc to suit the logic it is interfacing to (3.5V to 5.5V). The peripheral cells run directly from this supply. The CML matrix cells use a 0.95V supply and are fed via on chip series voltage regulators. If required, the regulators can have their own supply pin (Vreg), in which case the input supply voltage can be between 1.3V and Vcc to minimise power dissipation without compromising speed. Otherwise (like in the Sinclair ZX81 design) both are fed via the same power pin (the ZX81 ULA only has a single positive power supply pin).
Separate I/O voltage and core voltage - an old concept in electronics. But never knew it was used inside ZX81 ULA's. Very interesting info! 8-)
Btw. only thing such on-chip regulators do, is move dissipation from one local spot on the silicon to another. Unless you're talking VERY high-power transistor or similar, temperature will be fairly even across the IC die anyway.
As well as the regulator circuitry, a large power consumer is the peripheral cells.
Don't confuse power consumption with dissipation! For example if current flows out of an I/O pin @4.5V (with 5V supply), that pin's driver only has to 'burn off' (dissipate) 5-4.5=0.5V @ that pin's current. The remaining 4.5V @ pin current is dissipated where that current goes (read: not inside the ULA). In short: an IC's supply current * voltage is not EXACTLY the same as its heat dissipation. But in most cases, the difference (determined by current "sourced" or "sinked" through I/O pins) is not big enough to matter much.
1024MAK wrote:But changing the 7805 for a RECOM or similar switching regulator, or using a regulated 7.5V to 9V external power supply (* see note) is the better solution. A switching regulator produces hardly any heat. While a 7805 run with a lower input voltage of 7.5V will only dissipate half the amount of heat compared to when using a Sinclair PSU.
"Best" depends on what you're using as power brick, and your budget. Note that these type of regulators usually have ~80% efficiency, 85% is a very good number for a small switcher @5V output (never mind the datasheet :| ). A low-drop linear regulator can do better if input voltage is regulated too, and low enough. For example at 6V input, a 5V output regulator is 5/6 = 83% efficient (same as that switcher). If it can do 5.5V input, that goes up to 5/5.5 = 91% (better than switcher). Advantage of a switcher is the high efficiency across a wide input voltage range.
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