First Test of assembled BETA PCB looks to be an initial success!  Well at least it is in the analog mode via the composite output.

The ROM switch to go between PAL and NTSC parameters is also working, although I think I need to do some tweaks on the NTSC ones, but that'll happen in due time.

Meanwhile I'm still waiting for the JST 1.25 mm cable and connector to show up, which will allow me to run with the A/V-to-HDMI Converter installed. That will be quite exciting to say the least (hey I get excited easily, what can I say).

So all in all, not bad to get to this point in a bit over 2 months. Yes it was towards the end of May this year that I first downloaded Sobola's XEP80 schematics and began the process of backward engineering his schematic into a form I could use to eventually lay out a PCB from. Then the creeping featurism took over, and here we are today, although I don't really think the extra features are creepy at all, and should prove to be quite useful. Anyway I'll make this a short post and get out of here - stay tuned for further test results to come.

- Michael

It's gone through a bit of evolution since I first posted about it, and took a turn away from SMD in the process, now fully embracing THT components. This was done for a couple of reasons, one because of the added AV jacks the footprint expanded in such a way that extra space opened up that made sense for through-hole components to be used instead. And secondly it'll be more conducive for a DIY hobbyist to assemble the board, as well as greatly easing the troubleshooting of such. And even though the board has grown because of this decision, the new layout is still pretty compact at only 4.5" square - the same footprint as the 576NUC+ motherboard.

The addition of the extra AV jacks will facilitate all of the input possibilities that come with the A/V-to-HDMI converter. So now not only will the 80 column output be sent over HDMI, but so too will the 40 column stock video and sound.

To make this happen... an analog switch IC (MAX4619) will appropriately route the video signals, being toggled by a small tactile push button centered on the front side of the board. Each button press will switch between 40 and 80 columns, and then back again, with a dual stacked LED next to it indicating which video mode you are presently in. This will allow a single HDMI monitor to serve both video sources.

Let's pause for a minute and look at a preview image of the 'newest' 100% fully routed THT board layout. And for those that have been following this over at AtariAge, you'll possibly notice that I have moved the A/V-to-HDMI converter landing spot, so that it can now be flipped around 180 and have it's HDMI port facing the same direction as all the other jacks. This will become much more obvious when I post some pics of the real assembled boards.

Video and Communication Connection Breakdown

The JST 1.25mm x 8-pin male connector (J1) is to provide connection to the optional Wiistar WS-Z51 A/V-to-HDMI converter. It requires a double-ended cable with 8-pin female JST connectors to mate the two aspects together. Once connected, the 80 column output can be sent thru the HDMI port. And the stock Atari 40 column text output (as well as graphics) can also be converted to HDMI, with either being individually displayed at the press of a button.

Jumper block header (J2) is for configuration without an A/V-to-HDMI converter daughter board being present, so that the 80 column composite signal can be routed directly out through the yellow RCA jack to feed a standard composite monitor instead.

The three RCA (J3) jacks on the left provide the following inputs from left to right: Right channel audio, Left channel audio, and composite video (CVBS). The Mini-DIN (J4) jack provides an S-Video input. These analog A/V signals are only required if the A/V-to-HDMI converter is installed, and will get sourced from the Atari's normal video output jack using a suitable A/V cable.

And last but not least we come to the DB9 jack on the far right which is to be connected to one of the Atari's joystick ports to provide both serial communication and 5 VDC power.

Over the next couple of weeks I will be testing the newer 74 series High Speed CMOS chips in place of the older 74LS ones originally found on the XEP80. I'll also be testing the new lower power display RAM, and the lower power EEPROMS that will take the place of the factory ROMs. This is all aimed at extracting power for this board from the Atari's joystick port without overwhelming the stock power supply. If all goes well and the board+schematic are brought to an error free state, I will then have a small batch of boards made by JLCPCB for testing.

Update: July 22nd 2021 - All of the chips in my stock XEP80 baseline unit were replaced with their 74HCxxx counterparts that were proposed for the new design, as well as the newer SRAM and EEPROMS. After this change, power draw dropped from 430 ma down to 210 ma, making it practical to derive power solely from the Atari, while XEP functionality remained unaffected. Gerbers have since been sent to JLCPCB for sample boards to be manufactured.

That pretty much covers it for now,

- Michael

In June of 1987 Atari was preparing to release a piece of hardware to finally give the Atari 8-bit computer a universal 80 column text display, something that many felt would make it more usable as a business machine. Unfortunately it didn't end up being quite the wonder box in reality as depicted by the July 1987 Antic magazine article (VOL. 6, NO. 3). Instead people began to complain about it being slow, and in later years having serious over scan issues on more modern TVs.

However in spite of its bad reputation, there were those that liked it, and found it useful for editing code in Basic, the Assembler/Editor, and MAC65, as well as others who would go on to write extensive documents in the 80 column word processor AtariWriter 80.

I was one of those people that opted not to buy the XEP80 when it first appeared in the stores, instead saving my money for the new XE line of computers and printers that had arrived just a couple years earlier, and were quickly dropping into my price range. However over the years that followed, I always wondered what it was really like to use one of these mystery boxes, and if they truly were as bad as I had heard.

Well just recently I got that chance thanks to Bob Wooley of SLCC fame, that not only had one of these in his Atari barn, but ended up giving me 3 of them in various states of disassembly, and/or modification. We played around with them on his test bench for a while, with only one of them actually working. But what I saw was a video solution that rendered very readable 80 column text even on the tiny 9" CRT that we had it hooked up to.

So I took my new found treasure home, and continued fiddling with the one that worked over the next several days, and also discovered what was wrong with the other two that hadn't worked (bad firmware ROMs). As I tried out various things, I started to really like the possibilities, although I wasn't loving the over scan issues on my LCD. But thanks to Avery Lee (aka AtariAge member phaeron) creator of Altirra the Atari 8-bit emulator, I discovered that he had written a utility called XEPVHOLD.COM that corrected the timing chain parameters in the XEP to work much better with modern monitors, and boy did it ever!

Now for the Project

So long story short, I thought this might make for a cool reboot project, and started investigating the availability of the main display processor chip being used on the board (National Semiconductor NS405). Well it was no big surprise that a chip used in a 30+ year old design would be obsolete, and only available as surplus stock or pulled from other equipment. But amazingly after a very short search I found a great source for pulled chips at an incredibly cheap price, and in large quantities from a seller on eBay. So I pulled the trigger and bought 200 of them. Hey I told you they were cheap!

Having gotten that problem out of the way, I proceeded to backwards engineer the XEP80 with the help of Jerzey Sobola's schematic. And although his XEP80 diagram consisted of what should have taken 2 or more pages to cover, but all crammed on to a single sheet, it was remarkably accurate, only missing a capacitor, resistor, and some inline RF chokes. Thus using his diagram as a starting point, I began the process of drawing up my own schematics (3 pages this time), and took the liberty of specifying HCT chips to take the place of the original 74LS ones as used by Atari, and replaced the old ROMs and SRAM with modern CMOS ones as well, with the goal of running this directly off of 5 VDC Joystick power (the original XEP80 used a 9VDC wall wart). My schematic is now done, but I'm not yet ready to release it until I've really proven it out.

Next I started laying out a PCB, and continued my testing, some of which related to an alternative video output circuit I was experimenting with. It was during this phase that I discovered I could get a very nice centered image on an HDTV by using one of those inexpensive AV -to- HDMI converters. In fact it really was quite amazing how good it looked. So at that point things took a turn, and I decided to see what would be required in order to incorporate one of those AV2HDMI boards into my project.

Here's a look at where this has taken me (the white circles with the red 'X' inside shows where the AV2HDMI board will mount).

I decided to keep the analog video output as part of my design, and implement the AV2HDMI aspect as a daughter board stacked on top with it plugged into the CVBS video output jack. So first I had to extract the board out of one of those Chinese made converters being sold on Amazon and eBay for a very low price of $14-15 including FREE shipping.

The one I chose will convert either a CVBS (composite) or S-Video analog input to HDMI, and it also incorporates audio pass-thru to the HDMI output. The conversion of the Atari color video output into HDMI is less than spectacular when using one of these cheap converters, however in contrast the quality of the timing corrected XEP80 video looks quite remarkable - probably the best I've ever seen for the XEP80.

As it turns out, the board inside is very easy to extract, only requiring prying open a pressed together clam shell plastic housing. And conveniently it already comes with 4 mounting holes on its PCB, of which I was able to use 3 of them to mate up with my proposed XEP board design. The idea is to use 3 standoff's in order to clear the chips underneath. I don't plan on using the S-Video or audio inputs, but will retain them and tuck them inside whatever case is created for this project. They will be available as hackable possibilities for the end user to take advantage of if he or she so chooses.

So here's what that AV2HDMI board will look like mounted to my XEP80-II board.

The AV2HDMI board will get it's power from my board, and require a modified micro USB cable to do it.

The yellow composite input lead for the AV2HDMI gets plugged directly into a mating RCA jack on my board, making it ready to roll. All that's required is to plug a custom joystick style cable into the computer, turn it on, and boot the XEP driver.

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Click on the image to the right to get an idea of what this board combination can do on a modern HDTV when using Avery's modified video timing parameters and feeding through one of those Chinese video converters.

It's remarkably clear, with very legible text, and no distortions like one might encounter on an old CRT display. Basically this brings the XEP80 into the 21st century.
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My future plans are to incorporate Avery's XEPVHOLD parameters into the firmware ROM, assuming I can figure out how to do that. And since there are different requirements for PAL vs NTSC, I have implemented a configuration jumper that bank switches the firmware ROM, with the lower half containing code with NTSC parameters and the upper half having the PAL parameters. This way something like AtariWriter 80 will work correctly out of the box.

Well that covers it for now, but please check back for more news on the progress of this project.

- Michael