VT510 ROMs and PCB information

[paleotechnica]

I've been looking into emulating some of the more modern VT terminals in the VT5xx range and it looks like the VT510 is a bit of an unloved child in that range (possibly because it was a single-session, cost-reduced version?).

I bought a few bare boards off eBay to experiment with. It appears that it also uses a 512kB ROM like the VT520. The DEC integrated video/system chip has significantly fewer pins than the VT52x series - likely because it doesn't need to communicate with a colour generator, but also because I think that they had integrated the DUART into the main IC by this point. I haven't confirmed that at all, and have only taken a cursory look at the VT5xx PCBs themselves without seeing any obvious UART chips of any sort (should be easy to beep out once I have some time!).

The ROMs for the 510 series appear to be unarchived entirely AFAICT. I've got one with 23-032ED-00.bin and I've found a few other revs that I'll hopefully be able to dump shortly.

It appears that both the 510 and 520 have RAM and ROM expansion capability, but the 510's header has significantly fewer pins, likely because the 520's header may actually allow for a b/w -> colour upgrade (!).

Some very quick PCB pics attached for now.

 

[Terri Kennedy]

Some very quick PCB pics attached for now.

I'm betting on it being assembled in China (that doesn't really matter, other than it may explain component variations between boards). The Foxconn pull tab on the IDC cable has me leaning that way, but the SimSun font that practically scrams "China!!!" on the EPROM label proves it, IMHO.

 

[paleotechnica]

I'm betting on it being assembled in China (that doesn't really matter, other than it may explain component variations between boards). The Foxconn pull tab on the IDC cable has me leaning that way, but the SimSun font that practically scrams "China!!!" on the EPROM label proves it, IMHO.

Agreed.

Also interesting, this is the only VT4xx/VT5xx board in my hands that has a UV-windowed EEPROM under that label rather than a DEC-printed ROM part number. These _might_ be new/old-stock replacement boards for field service that have manually-socketed upgrade ROMs.

 

[davidrg]

It appears that both the 510 and 520 have RAM and ROM expansion capability, but the 510's header has significantly fewer pins, likely because the 520's header may actually allow for a b/w -> colour upgrade (!).

The VT520 has a mono CRT built-in same as prior models (excluding the VT340 and VT240 of course), while the VT525 takes an external VGA display which makes upgrading a VT520 to colour seem unlikely. So if you run across any VT525 boards they'd probably be interesting to look at as I imagine they're probably quite different from the VT510/520.

As for RAM expansion, I ran across this post a while ago that mentions it expanded page memory; would certainly be interesting to find out if that is true and just what sort of effects it had on the paging options!

 

[MiaM]

Interesting!

I wonder what the return-of-investment was on that terminal-in-a-chip IC?
Did DEC except terminals to live on for much longer than they did?

 

[davidrg]

Boundless was still selling newly manufactured VT520s until about 10 years ago - I wonder how that worked with the custom chip.

 

[paleotechnica]

I've been digging into the 5xx firmware and it's a fascinating upgrade from the 420. The code has clearly been rewritten drastically, and it's entirely possible a lot of the development moved to a higher-level language like C.

The custom ASIC is also *much* more functional. It appears that it does significantly more complex video processing which allows for the 8051 to be a little less busy and less efficient overall. This is more complex from an emulation point of view, but I think it's still doable. So far I've found where it handles the PS/2 protocol, the UART(s) and some early signs of how video mapping is handled.

The VT520 has a mono CRT built-in same as prior models (excluding the VT340 and VT240 of course), while the VT525 takes an external VGA display which makes upgrading a VT520 to colour seem unlikely. So if you run across any VT525 boards they'd probably be interesting to look at as I imagine they're probably quite different from the VT510/520.

As for RAM expansion, I ran across this post a while ago that mentions it expanded page memory; would certainly be interesting to find out if that is true and just what sort of effects it had on the paging options!

I've actually got some of the expansion cards on the way - a 510 one (which appears to be a ROM) and 520 one (which appears to be RAM). I'll report back on how they function. I would be interested to see if there are additional page memory options automatically unlocked with it.

Interesting!

I wonder what the return-of-investment was on that terminal-in-a-chip IC?
Did DEC except terminals to live on for much longer than they did?

Boundless was still selling newly manufactured VT520s until about 10 years ago - I wonder how that worked with the custom chip.

I guess the Toshiba gate arrays in the 510/520 were masked gate array parts, so it's possible that the production for them continued into the 2000s. They had a US plant up until '99 from what I can see (https://www.eetimes.com/toshiba-consolidates-asic-operations-shutters-u-s-gate-array-fab/) and the press release suggests that they consolidated rather than shutting down production.

As this is _really_ the only custom part on any VT5xx series (likewise, the video chip is the same unique part for the VT420), it's also possible that DEC ordered a fairly large backlog to continue production around the time of shutdown which allowed boundless to sell through the final stock.

 

[davidrg]

Did you get around to testing out the expansion cards? The original product announcement seems to say that you expand page memory from 9 to 20 pages with a cartridge - I guess that's what the RAM cartridge you've got does.

And there is this post (from the guy whose name is down as the approver of DEC STD 070) looking for people to test a ROM cartridge that adds a bunch of extra terminal emulations to a VT520 which is interesting - I wonder if it ever turned into a sellable product, or if any prototypes survived.

 

[paleotechnica]

Did you get around to testing out the expansion cards? The original product announcement seems to say that you expand page memory from 9 to 20 pages with a cartridge - I guess that's what the RAM cartridge you've got does.

And there is this post (from the guy whose name is down as the approver of DEC STD 070) looking for people to test a ROM cartridge that adds a bunch of extra terminal emulations to a VT520 which is interesting - I wonder if it ever turned into a sellable product, or if any prototypes survived.

Not yet - got busy recently but they're sitting on my shelf of things to dump. I am curious to see what's on the 510 ROM.

I started down the path of emulating the 510 and 520, which are far more complex beasts and much more integrated than the 420. The architecture between the the 510 and 520 series is _very_ similar.

I never came across any 520 expansion ROMs, but that would be a fascinating find.

 

[davidrg]

Aside from ROM upgrades, and RAM upgrades (photos/info), it turns out there is a third use case for the cartridge slot: copying settings between terminals!

EZ-SetUp Cartridge: announcement, instructions (PDF)

I guess all these things probably used the same PCB. The memory cartridge I have has space for four chips and three resistors, with only one chip (memory) and resistor populated.

 

[pbirkel]

I wonder if any of your findings apply to the VT525?
EK-VT520-RM_VT520_VT525_Programmer_Information_Jul94.pdf treats them as essentially the same.

 

[davidrg]

I wonder if any of your findings apply to the VT525?
EK-VT520-RM_VT520_VT525_Programmer_Information_Jul94.pdf treats them as essentially the same.

I suspect so. The product announcement for the VT520 and VT525 seems to suggest that the memory cartridge was available for both , though it's hard to be sure as Google groups destroyed the formatting.

The options must have been different parts for the 510, 520 and 525 though given the expansion connector on the 510 is apparently smaller and I think on the 525 the cartridge must slide into the slot on the front so the connector will be on the end of the PCB rather than on the component side.