Multi-display setup

[Kevin Buhr]

I'm still trying to figure out the optimal number of displays for a RC2014. I'm thinking 6? If so, I'm halfway there.

From slowest to fastest, the PCBs for my parallel mode TFT interface (lower left corner) just arrived today, though I haven't gotten further on the software side than writing a bitmap font driver. With a resolution of 240x320 and minimum 2 writes per pixel, it maxes out at just over 1fps. The serial terminal on the right is running a game of Life written in 8080 assembly. It uses VT100 cursor positioning to selectively update the display (though somewhat suboptimally) and gets around 2 fps at 115200 baud. The display in the middle is a "multicolor mode" landscape on my TMS9918A video card. It is moderately downsampled from the original (see attached) but still very inspiring!

Hope everyone else is having a great July 4th (or just "July") weekend!

 

[Bill Shen]

I think 3 screens may be a good software development setup.  One screen for console interface, one screen for the application, such as the game of life, and third screen to display the real-time variables associated with the running application.  Current RC2014 hardware can support such setup,  but I don’t know about screens 4, 5, and 6.

[MartinR]

That's an impressive video set up - and a long way from mine.

I've started thinking about some form of video module for my RC2014 set up. I currently use Tera Term to my desktop machine or an RP2040 VGA Terminal from https://z80kits.com/ - a great piece of kit, though is hardly period. Both are limited to 115kbps across a serial port and so the speed of a video module appeals. However, I've been getting confused reading all the postings, designs etc

I'm looking for something that will output to a spare VGA LCD flat screen that I have. I don't have any CRTs, and being in the UK, certainly nothing with NTSC. I'd like to stay with period technologies as best I can, and RomWBW support is essential. So - would someone be able to advise me of the suitable option/s for me?

Many thanks in advance - 

MartinR

[andy....@googlemail.com]

I’ve just built a TMS9918 card, and with a cheap scart to hdmi adapter it seems to detect the NTCS input.  Just trying to get it to work with ROMWBW now!

PS I’m in the uk also

[andy....@googlemail.com]

*NTSC

[MartinR]

Hi Andy -

Thank-you for your encouraging reply!

Could you share a few more details?

Which TMS9918A module did you go with? And did you buy it as a kit, or a bare PCB and then source your own components?

My old Dell VGA monitor has VGA D-Sub and DVI inputs - so no HMDI. I daresay other adaptors would be available?  The documentation for the monitor I have says that it supports 640x480 (and higher) at 60Hz-75Hz. Is your monitor able to support 50Hz? Or did you tweak the TMS9918A (if that's at all possible), or does your adaptor increase the frame rate (seems unlikely)? 

These are some of the uncertainties I have and which are preventing me coming to a decision....

Thanks for any help.

MartinR

[Alan Cox]

On Sun, 7 Jul 2024, 01:45 Bill Shen, <coinst...@gmail.com> wrote:

I think 3 screens may be a good software development setup.  One screen for console interface, one screen for the application, such as the game of life, and third screen to display the real-time variables associated with the running application.  Current RC2014 hardware can support such setup,  but I don’t know about screens 4, 5, and 6.

I currently have 2 serial, a tms9818a, an ef9345, a propeller based card and a TFT attached plus 4 spare serial. The cards take few IO  ports so there is no obvious limit I can see 

Alsn

[andy....@googlemail.com]

I’m using https://peacockmedia.software/tms/TMSmodule.pdf I have set it to ports 08/09 as per the pdf.  Then needed to modify the ROMBWB source just updated the Calco ports in the source file tam.asm to 08 and 09.  I now have console output on my screen!

[Mark T]

Most TVs in the UK will support NTSC or PAL, so should be no need to be concerned about the TMS9918A composite output to a TV.

[Kevin Buhr]

Hi, MartinR,

I'm in the US, but I'm using this composite-to-HDMI adapter from Amazon: https://www.amazon.com/Converter-BD-Composite-Adapter-Blue-Ray/dp/B08W98BD6L. It cost $10, and it's built exactly like it cost $10, but it works. A very similar looking $10 composite-to-DVI adapter is also available (https://www.amazon.com/Video-Converter-Adapter-Composite-Set-Top/dp/B0BJKD5W32), so that might suit your needs. The biggest problem with these adapters, in my limited experience, is that they're cheap and flaky on the initial sync.  (Bizarrely, mine usually needs the HDMI side unplugged and replugged to sync properly, even though the HDMI side is working fine, since it can display its "No signal" error message.)

Once they're synced, they work great, but this means that when you build your TMS board and don't get a picture on the first test, you don't really know if it's your board. It also seems like the TMS boards draw a fair bit of power and are very sensitive to a less-than-perfect 5V supply, so you might have built a perfectly good board that doesn't generate a picture because of some combination of imperfect power supply and a cheap converter.

For my part, I built my board from a bare PCB and sourced components. I had planned to buy a kit but could only find fully assembled boards and wanted to assemble it myself. Everything was easy to source (from Digikey US) except the TMS chip itself. I first tried a cheap Amazon seller with no reviews and got a desoldered and relabeled chip with one pin completely missing and another pin fractured. For my second attempt, I tried a more expensive source on eBay (https://www.ebay.com/itm/135111542788) and got what looks like a new chip in perfect condition. I estimate that the cost in parts other than the TMS chip and PCB was around $20. Factoring in the TMS, PCB, and shipping costs, my total cost was probably around $60-70. Fully assembled and tested kits are available on Tindy from a UK seller (https://www.tindie.com/products/shieladixon/tms9918a-video-module-designed-for-rc2014/) for $69+shipping, so that seems like a good deal if you don't really care if you build it yourself.

The TMS9918A chip only generates composite NTSC. There is a TMS9929A (not to be confused with the TMS9928A) that generates a PAL-compatible signal, but it outputs YPrPb instead of composite. The chips are software compatible and *nearly* pin compatible (even taking the same crystal), except that Y is output in place of the composite video, and PrPb are output in place of CPUCLK and EXTVDP. Since JB's board only routes these latter two pins to an external jumper, you could probably stick a TMS9929A chip in the board and have it function, generating a 50Hz monochrome Y signal on the RCA jack. I don't know if anyone's tried this.

Kevin

[MartinR]

Thank you Andy, Mark and particularly Kevin for a great deal of useful information.

Very useful to know that VGA monitors in the UK should be fine with a 60Hz signal. And that suitable (proven) adaptors are readily available at low cost from the ubiquitous Amazon.

I've checked out the PeakcockMedia module, and it seems that the Tindie seller of the JB Langston modules and PCBs has only PCBs for sale, which suits me perfectly as I've enjoyed building all the modules I have. However, unfortunately that seller won't ship to the UK. https://www.tindie.com/products/mfkamprath/tms9918a-video-card-kit-for-rc2014/ I can go Googling for an alternative seller of the PCBs, but if someone knows of one (assuming there is one) then it would be helpful. Or maybe someone has a spare they don't need for a reasonable consideration?

A useful tip about an adequate PSU. I had similar issues with my floppy drive pulling the 5V low enough to cause problems. I now have a 5-Amp switched mode PSU supply the 5V to my system. It has plenty of spare capacity and so it should be OK for me to add a video module.

I had read that there is a TMS9929A chip which first attracted me because of its PAL capability but after reading the helpful comments above it seems that I shan't need a PAL chip. Therefore, I'll go with the TMS9918A as that's been proven to work, and work with RomWBW and maybe one day get the PAL variant to have a play with.

Thanks all - all the help and information is much appreciated.

MartinR

[Kevin Buhr]

Hi, MartinR,

Because I had my board made by JLCPCB, I've got four spare boards, but it's no easier for me to send you one than it is for Kamprath Hacks, I guess. You could try contacting MIDI IN, the UK seller I mentioned, via the "Contact Store" link (https://www.tindie.com/stores/shieladixon/) and see if she has any bare PCBs she'd be willing to sell. If you're stuck, I've attached the Gerber zipfile I used for JLCPCB. JB also has a Gerber zipfile linked from his repository under "Assembly Instructions" here: https://github.com/jblang/TMS9918A that would almost certainly work, but I nudged a few traces in his design after reviewing the JLC tools' errors and warnings and regenerated the Gerbers, so the zipfile I used was a little different. Ordering from JLCPCB is straightforward -- just upload the zipfile (which auto-configures all the technical settings), accept the defaults (or change the PCB color to "Blue", if you want), and submit the order. If you use their DFM tool (under Gerber Viewer -> DFM check), note that it will misidentify vias as annular ring errors. There are also lots of bogus silkscreen errors that you can ignore, and there are three solder mask errors that I missed fixing but they turned out fine on the final boards.

The price for a job this size is a ludicrously low $2 for 5 boards (the minimum quantity) plus shipping. That's $2 for all five boards, not per board. I didn't actually believe it until I finally checked out. They gave me a $10 off coupon that applied to shipping, so I chose a fast $20 shipping option. I ordered on June 21 and got the boards on June 26, I think.  (This was all for shipping to Wisconsin.)

I really don't know how they make money. On a different board that -- again I have to emphasize -- I was having custom manufactured for $2 plus $3.50 for "slow shipping"), customer support actually contacted me about a potential issue before continuing with my order. For $2... Weird. I guess this is a golden age for custom 2-layer PCBs. The $2 is supposedly a "special offer" compared to their regular price of $4, but I've used it for two boards now, and I'm not sure when/if it expires.

I'd still prefer to order from Tindie sellers where possible, if only to cut down on the environmental impact of having 4 extra lead filled boards laying around, but Kamprath Hacks went on a long vacation just before I decided to place my order, and the other board was a new design. Anyway, JLCPCB is an option if you can't find a UK seller.

Kevin

[Dave White]

I've just ordered up all the parts to try one of these:

https://forums.atariage.com/topic/367656-introducing-the-pico9918-a-tms9918a-drop-in-replacement-powered-by-a-pi-pico/

If it works as advertised, it'll give TMS9918 compatibility with VGA output., so should hopefully work with ROMWBW out of the box. It needs a "special" version of the Pico, and they are currently on their way from Ali Express, and the circuit board uses surface mount resistor arrays, of which I have none, so they are on their way too. Hopefully I can put one of these together in the next couple of weeks and check it out.

[MartinR]

Hi Kevin -

Thanks for your further helpful comments.

Good idea to see if MIDI IN has any boards that they'd be will to sell to a UK customer, though it does seem to be kits for this module that they are selling.

Many thanks for your hints and tips on getting these boards manufactured through JLCPCB, and also for your tweaked Gerbers. I'm thinking that I'll likely need to go down this route, and like you will end up with spare boards. I did exactly the same for my floppy-disk controller after I had a frustrating time trying to hand wire one and which ended in failure.

I suspect that JLPCB will charge higher prices for shipping to the UK, and I think that I used up my introductory offers on my floppy controller PCB(s).

I'll let you know how things progress, but I really do like the idea of direct hardware controller video and a serial keyboard. This is the same sort of configuration that my SC84 CP/M computer had back in the mid-1980s, though that used a 6845 CRT controller. This was a design published in 'Electronics & Wireless World' magazine in 1984, and which can been read at https://www.computinghistory.org.uk/det/22148/SC84/

Much appreciate your help - thanks again.


MartinR

[MartinR]

Hi Kevin - 

Quick update.

I've done as you suggest and gone to JLPCB and ordered up some PCB using the Gerbers you had kindly attached. Admittedly I've opted for the slowest delivery option available to keep costs down, but the total cost was mind-numbingly cheap. Discovering this has really incentivised me to have a go at designing my own PCB which was something I was half-planning to do as vanity project in the winter months.

Thanks -

MartinR