A Softy 2 lives

[SiriusHardware]

I don't see the composite signal output on the circuit diagram so I'm wondering if someone has just tapped that off from the input to the modulator? If so, sometimes that works and sometimes, for example with the ZX81, it doesn't produce a very conformant composite signal and an additional buffer is required.

I notice on the diagram that there is an 'optional' resistor from the modulator input down to GND - I haven't looked through the text yet to see when you would or would not fit that resistor, or what value it should be if fitted.

[AnalogueMan]

This is all remarkably fascinating and well beyond my pay grade. I might even learn a few things about digital stuff following this

[Timbucus]

Originally Posted by AnalogueMan

This is all remarkably fascinating and well beyond my pay grade. I might even learn a few things about digital stuff following this

Well the above fault was analogue which is way out of my comfort zone and Sirius was correct that back on the CRT all the funny artefacts are gone; the repeated cursor, corrupt location on the screen and the extra columns to the left and right.

It is as he surmised just tapped off the lead going into the modulator so it may need some help to become a usable composite connection.

Right back to working out how to use it - I will just have to accept the poor TV for the moment.

[SiriusHardware]

You may just have to bow to the inevitable and get yourself an era-appropriate 12" B&W TV to run your MK14 VDU replica, ZX81s and now the Softy 2, and no doubt others, into.

What would be absolutely perfect would be a Ferguson 3845, the 'classic' simple 12" portable with a simple front panel tuning control to tweak every now and then when those ASTEC modulators warm up and start drifting gently off frequency.

https://www.snellingsmuseum.co.uk/ar.../ferguson-3845

[Timbucus]

Yea - I think you are right...

[AnalogueMan]

Your alternative option would be to build a video buffer stage for the output. Plenty of nice analogue pitfalls there though...

[SiriusHardware]

Most if not all composite video inputs are internally terminated with 75R which is quite a low resistance load. Monitors made specifically for CCTV are nearly unique in having the 75R termination load switchable so that several monitors can be chained on one output with the load only switched 'on' on one of them (which is why I asked whether Tim's monitor had such a switch).

Looking at the Softy video-out circuit I would say it has little hope of maintaining its video signal into a 75R load - the input impedance of the modulator is much higher than 75R and the video circuit is designed to drive that, not a 75R composite input.

This is quite a common problem in the retro computing world and there are plenty of very small off the shelf video buffer PCBs which are aimed at solving precisely this problem. There won't be anything specifically made for the Softy machines but one intended to solve the same problem on a ZX81 may work.

Early computing / video game devices from this era generated very crude video signals which the TVs of the day happily coped with, but more recent devices, and especially flatscreens, often find themselves flummoxed by the signals from these old devices.

One well known example is the early to mid production period ZX81 in which the system chip generated a video signal without a 'back porch'. Later TVs sample the level of the 'back porch', which follows straight after the rising edge of the sync pulse, and from that they determine what should be regarded as 'black' level for the rest of the line.

On the ZX81 (early to mid versions) the video signal goes straight from the rising edge of the sync pulse to peak white level, because the normal display of the ZX81 is black characters on a white background. A modern TV samples what should be the back porch level and instead finds peak white, so it sets the black level relative to that, resulting in a very, very, dark screen.

On late ZX81s the ULA IC was modified so that it did generate a back porch.

For the Softy, it may not be enough just to build a buffer circuit, it may also be necessary to resinstate the missing back porch, if indeed it is missing. Some of the more high end composite buffer circuits for the ZX81 also include circuitry to do this, but they rely on the fact that there is a broad band of unused screen area between the left hand side of the screen and the beginning of the 'active' screen area. I'm not sure if the Softy's video signal has any such dead space available to insert a back porch into.

[Realtime]

I've been creating a simulation of the SOFTY2 output circuit but ran into trouble when I remembered that modulators present themselves as non-linear loads - for the UM1111 it's 700R at sync tip [0V] and 4K at peak white level [1.8V]. My modelling is not good enough to create this non-linear load but a photo of the output waveform would allow me to generate a waveform simulation that can then feed a correcting buffer to provide a more standard 1V p-p video output.

Tim, any chance of putting a scope on the input to the UM1111 modulator and taking a photo?

Just for info the UM1111 input characteristic is significantly different to the more common UM1233, which needs a DC offset of about 2.5V on the sync tips. So a video output buffer specific to SOFTY1 & 2 is the likely best solution.

[ortek_service]

It's great to finally have access to a Softy 2, after us being so close to getting full details on this when OneWatt started a thread two years ago after he'd found a couple like-new: https://www.vintage-radio.net/forum/...d.php?t=179674
But unfortunately he hasn't posted since a short while after this, and ChrisOddy wasn't able to get a reply from PM to him.

It always seems strange how much rarer the later Softy 2's now are, compared to the original Softy-1, when they were sold by Maplin etc.
- See attachments on my post (No.74), here: https://www.vintage-radio.net/forum/...=179674&page=4
Especially when the Softy-2 was in a much more-convenient squarer form-factor with an enclosure and a smaller PSU, so needed less space to be able to use and less likely to get physically damaged than bare boards.

The Softy-2 also had twice as much RAM, but did have the disadvantage that it no longer supported the older 3-rail EPROM's that the Softy-1 had, and I never saw an official adapter available for it, to support these legacy EPROM's - Only adaptors to allow later larger EPROM's to be used, by bank-switching into the Softy-2's RAM-mirror area (Like with using 2732's on the Softy-1)
But it seems Dataman had reached the limitations of the SC/MP, so they switched to a Mask-programmed low-power (CMOS?) Toshiba Z80

I wonder how practical it would be to add the 3-rail support back onto a replica version of the Softy-2 or just using an external adaptor board. But would need to check what device programming timings are supported in the (EP)ROM for it.
Or Maybe upgrade the RAM of the Softy-1, so that it could also work like a Softy-2, as it seems most of the circuitry was unchanged between these.

[ortek_service]

Originally Posted by Realtime

I've been creating a simulation of the SOFTY2 output circuit but ran into trouble when I remembered that modulators present themselves as non-linear loads - for the UM1111 it's 700R at sync tip [0V] and 4K at peak white level [1.8V]. My modelling is not good enough to create this non-linear load but a photo of the output waveform would allow me to generate a waveform simulation that can then feed a correcting buffer to provide a more standard 1V p-p video output.

Tim, any chance of putting a scope on the input to the UM1111 modulator and taking a photo?

Just for info the UM1111 input characteristic is significantly different to the more common UM1233, which needs a DC offset of about 2.5V on the sync tips. So a video output buffer specific to SOFTY1 & 2 is the likely best solution.

The UM1111 was the rather crudest of modulators, using a single transistor, with no output buffering. So frequency-drift on these was apparently rather more than on the much-more commonly encountered (now also discontinued, but obtainable from lots of old home computer boards that used it - if rest of board is too far gone to be viable to restore) later UM1233 etc.

ChrisOddy has made his slightly-enhanced replica Softy-1 PCB design accept both of these Modulator types - Although some component value changes are required, to make the levels right for the exact-type being fitted.
He also added an RCA-Phono socket, for a more convenient these days / better-quality composite video output. I can't remember how well buffered this was / if it can be used a the same time as having either modular fitted, but fuller details should be on his webpage: http://www.theoddys.com/acorn/proms_...1/softy_1.html

With also details about the Softy-1 and dump of its Character generator PROM, here: http://www.theoddys.com/acorn/proms_...1/softy_1.html

The 74S287 PROM is also quite difficult to find NOS of at sensible price, although there is a Tesla MH74S287 version, at a reasonable price (Rather less than postage from E.Europe) from TVsat etc. But could probably also use the 2x capacity 74S571, as used for MK14 OS etc, being as MH74S571's cost about the same as MH74S287's and program both lower / upper halves with the same content (It does also give you a backup version in it, in case of a single bit failure - If that ever occurs rather than whole-IC failure?).

[ortek_service]

Originally Posted by ortek_service

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ChrisOddy has made his slightly-enhanced replica Softy-1 PCB design accept both of these Modulator types - Although some component value changes are required, to make the levels right for the exact-type being fitted.
He also added an RCA-Phono socket, for a more convenient these days / better-quality composite video output. I can't remember how well buffered this was / if it can be used a the same time as having either modular fitted, but fuller details should be on his webpage: http://www.theoddys.com/acorn/proms_...1/softy_1.html
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I found I'd actually posted the same link twice and Chris's Replica Softy-1 webpage is actually linked from that one / can be accessed directly from here: http://www.theoddys.com/acorn/replic...a_softy_1.html

I've been looking again at the original Softy-1 circuit, and what Chris has done on his (slightly more versatile video output options) Replica version.

It seems the main difference between the UM1111 and UM1233 video-input requirements is the DC-bias level, so different resistor values are required on the DC-biasing potential-divider on Chris's replica, depending on which one s fitted. Although the UM1111 also has a 220R series-resistor, which I presume will (in conjunction with UM1111 input impedance) attenuate the input signal a bit. I do recall Chris having to 'scope both UM1111 & UM1233 fitted options, in order to come up with the values detailed on his circuit, to ensure DC-bias & level was correct for the one chosen to be fitted.

Unfortunately getting hold of detailed spec's on Astec Modulators etc. always seemed difficult, with Astec Datasheets / Databooks - Particularly covering their modulators - seemingly harder to find than Softy-2's now are!
I do recall when buying them new, that you sometimes got an instruction sheet / maybe internal circuit (People have reverse-engineered some on some webpages, possibly thinking of re-making some).
But I did re-discover a good "The Care And Feeding Of Video_Modulators" article (written with input from someone at astec) that covers and compares the various types in the Mar-May 1986 issue of the Maplin 'Electronics' magazine - available here: https://worldradiohistory.com/UK/Map...6-03-04-05.pdf
IIRC, I'd previously highlighted this to Chris, who used it for ensuring input conditions were correct, but I can't find it on his website's useful data etc, so I've also extracted these pages as a standalone-pdf, plus attached here for convenience.

Regarding the Composite video output he'd added, he just took another tap via a 75R resistor, directly from the output emitter-follower video-buffer that the Softy-1 uses to combine all the separate CVBS to then feed into the modulator. His output is DC-coupled, to save requiring a fairly-large (to avoid too much LF roll-off into 75R) AC-coupling capacitor on the output. But I'd previously discovered from this very-useful article on video-signals (also showing 'Back Porch'): https://www.analog.com/en/technical-...o-signals.html
"Consequently, video-equipment makers have a tacit agreement to AC-couple the input of their equipment, and DC-couple the output—requiring the next stage to re-establish the DC component (see EN 50049-1 for PAL/DVB [SCART] and SMPTE 253M section 9.5 for NTSC, which allow a DC output level). Failure to establish such a protocol leads to "double coupling," where two coupling capacitors appear in series, or to a short where there are no capacitors. The sole exception to this rule is battery-powered equipment, such as camcorders and still cameras, which AC-couple the output to minimize battery drain."

Although I'd also discovered some small Video-Buffer Amp IC's, that incorporate 'SAG' correction feedback, to allow around 1/10th of the normally required AC-coupling capacitors to be used: https://www.analog.com/en/products/ada4430-1.html or direct pdf of it
https://www.analog.com/media/en/tech...eo-signals.pdf

Unfortunately, the Softy-2 seems to have deleted the emitter-follower buffer stage! (only to save a few pence?) So there isn't a nice low-impedance output to tap the video signal from. But could probably copy details from circuit of original Softy-1 / Chris's replica, and re-insert a buffer, built on a small piece of veroboard etc into the video-path to the modulator.

[ortek_service]

I assume the Softy-2 still used the original UM1111 type modulator ?
- The Softy-2 circuits don't give its type number and I haven't seen a good picture of that area of the board so far.

The 'Dataman Softy-2' manual strangely only has the Softy-1 photo (in colour on the cover) - even though it mostly covers the Softy-2! (Until I'd got to see inside manual after Tim had now kindly scanned it for us - but unfortunately it appears his copy has rather variable print quality between the pages - I'd assumed they gave you both a manual for the Softy-1 and maybe a supplement to cover the Softy-2 differences)

This 'Softy-2' manual also says you need to use a Softy-1, to program 3-rail EPROM's, so I guess they never planned to have an adaptor for legacy ones and must have carried-on selling the Softy-1 (which I recall was rather cheaper, especially in kit-form that the Softy-2 manual also shows inside) at the same time as the Softy-2, so that wasn't really a complete upgraded replacement for its predecessor (that seemed to be the case with the S3 / S4).

I've never seen an actual 'Dataman' branded Softy-1 manual, as the only Softy-1 (Construction & Use) manual I've seen - like one Chris had scanned: http://www.theoddys.com/acorn/proms_...01%20Manual%20[9].pdf
only has GP Industrial Electronics Ltd. address etc, and early adverts only mentioned 'Softy' as company name to write to (Although I think 'Dataman Designs' was also included in brackets on some later ones?)
So it seems Dataman was subsequently-formed and carried-on with the Softy-range development, with GP going a different path with their EP4000/8000 ((Also originally SC/MP-based) more-expensive programmers.

[ortek_service]

I also see that the Softy-2 has an extra 7-buttons on its keypad, with many of the shift-functions moved to different keys / positions.
So although the video h/w and memory map / many of the main IC's seem to be the same, unfortunately just swapping the firmware EPROM between these, wouldn't work out too well with the different keyboard mappings!
I wonder if the Softy-2 did offer any useful extra features in the firmware / newer keyboard layout was that much better, or whether staying with Softy-1 plus its single-rail EPROM adaptor board would be better?
- Except for only half the RAM, and whilst adding more shouldn't be too difficult, the firmware would need changing a bit to make it operate more like the Softy-2's RAM-size slots.
Maybe a Softy-1E/2E would be ideal, that combines the best of both versions?

[Timbucus]

Apologies for the delay in getting back on the Softy2!

I tried my Sanyo monitor and with some adjustments it is pretty usable with the Softy2 although as you can see from the cursor it does replicate the first few bytes at the end of the line...



...and you have to look behind the mask to see the very bottom row of memory! No external picture height adjustment

My google drive linked above now has photos of the PCB both sides and the bottom of the case. The clips were really hard to get out - so I found the ideal tool (justifies why I keep everything )



Be careful if you do take one apart the clip on the bottom right of the keyboard is gripped by the Glue from the KB cover so it lifts when you push it through - I have left it in with the pin just pushed high for the moment in case I have to strip it again.

It is the UM1111 as you surmised. Here are a few captures (DC Coupled) from the scope as requested (no monitor attached obviously...)

[Timbucus]

Just a quick update I struggled to find non 12v 2732 but, found two - confirmed one was blank by copying its contents to the buffer on Softy2 with SHIFT and COPY to see all FF

Used SHIFT and FIRM to copy firmware to ram buffer.

SHIFT and BURN to burn the lower half of the 2732 with the Softy Firmware (the bottom brown slider selects low or high for A11) - that auto does a compare and showed OK!

Finally to play with the COMPare I zeroed a few bytes in the RAM buffer and did the COMPare again it it nicely highlights the bits I zeroed.



DEF to define a block (which uses the highlight function) and MOV to move it around also seems to work to edit the RAM buffer. There are some interesting features in the firmware - like the ability to find the next three FF and shift code around. Calculate offsets using two cursors etc.

[Buzby123]

Its been 40 years or thereabouts since I used Softy, and my memory is a bit vague.

However, I do seem to remember the 'repeated righthand' characters. My understanding is that it was not a TV incompatability, but a quirk of the video generator RAM decoding.

If you count the characters, the repeat consistently happens after the 16th byte. Too much of a coincidence methinks.

Anyway, its great to see one running again.

Cheers,

Buzby

[ortek_service]

I've just spotted a review on the Softy(1), in a PCW (Jun'80) magazine, that I hadn't seen before. Softy-1 threads all now seem to have been closed, so rather than try to re-open / start a new one, I've attached a copy here for info - As quite a bit of it will be relevant to the Softy-2 as well (especially their need to tweak their TV's scan adjustments, to see all of the display!)

I've also left some of the PCW magazine's pages following this, on PSU-design, in the pdf for interest - I never realised that PCW went into so much Electronics design detail, but looks like there was a lot more cross-over with Electronics magazine back then.before they specialised much-more.

[SiriusHardware]

Here are a few captures (DC Coupled) from the scope as requested (no monitor attached obviously...)

Difficult to say from that whether there is a back porch immediately after the sync pulse because of all the wibbles preceeding the actual video output on the active part of the screen. The 'height' of the video looks awfully limp in proportion to the size of the sync pulse which is why the display looks washed-out and low contrast. It probably looks even worse when the monitor is connected.

I have an idea - not sure if you will like it - turn off the Sanyo monitor, disconnect the Softy from it and measure the DC resistance from composite signal in to GND. If the resistance is actually 75 ohms (it often is) then there may be a 75R termination resistor on the PCB near the composite - in socket on the monitor.

If there is, you could try raising the value of that resistor so that the Softy's video circuit will no longer be driving a load which is too low an impedance for it to drive.

Secondary to the problem of the load impedance being too low is the problem that the video signal being fed to the modulator intentionally does not have the same proportions / balance between the tip of the sync pulse, black level and peak white. As Realtime mentioned an 'ideal' buffer circuit will not only buffer the output but it will re-size the various elements of the video signal relative to each other so that they conform to the correct spec for a composite video signal.

[ortek_service]

Originally Posted by ortek_service

I've just spotted a review on the Softy(1), in a PCW (Jun'80) magazine, that I hadn't seen before. Softy-1 threads all now seem to have been closed, so rather than try to re-open / start a new one, I've attached a copy here for info - As quite a bit of it will be relevant to the Softy-2 as well (especially their need to tweak their TV's scan adjustments, to see all of the display!)
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Whilst recently at Bletchley Park's TNMoC, I did spot an original Softy-1 on display - Maybe one of those previously discussed at the start of this (now closed) thread: https://www.vintage-radio.net/forum/...d.php?t=194874 - In post: https://www.vintage-radio.net/forum/...9&postcount=17


This one had an unlabelled & uncovered windowed UV-EPROM IC. So leaving that out in daylight for years may not be preserving its contents too-well! (I wonder what version they have in this, as until a couple of years ago there were no copies to be found preserved on the 'net, until ChrisOddy managed to borrow someone's to read / fix it whilst at it)

And I've attached a photo of it (Inc. zipped-up copy, to not get compressed more) here, for reference.
- There's also some unusual items behind it, inc. a ?GP Ind. EPROM-Programmer board for ??
And an 'Anamartic' Sinclair-offshoot company Wafer-Scale Integration Solid-State memory board:
https://www.computinghistory.org.uk/...artic-Limited/
https://www.computinghistory.org.uk/...c-Wafer-Stack/

[SiriusHardware]

That reminds me, - Tim - have you now been able to fully test out that Softy 2 you were lucky enough to acquire a little while back? I recall you were having trouble finding a co-operative display for it but you seemed to have found a way around that.