800XL Deficiencies?

[Daedalus2097]

It's pretty well known that the 800XL's video port is missing the chroma signal, and that it's a simple mod to put right. But I was recently toying with the idea of experimenting with hardware on the PBI. (Don't get excited, it'll probably come to nothing). However, I found that the PBI connector on the 800XL is missing a 5V supply, which greatly restricts what can be done without running additional cables to the SIO or joystick ports. Like the chroma, it's a simple mod to add the 5V (which is present on the 600XL), but are there any other similar omissions on the 800XL that I've not met yet? And has anyone actually added the 5V to their 800XL's PBI, or is there no point because no hardware appears to use it?

[xrbrevin]

something similar occurred with the 1200XL - the SIO port was missing its 5v connection.

i wonder if it was left out during development and they forgot to put it back before the final draft?

[Rybags]

Some memory expansions will be deficient due to not supporting Antic extended banking.  But that's not the fault of the base machine really.

 

I added the +5V.  IDE +2 needs it and if you're not running a mechanical drive which would justify using an extra PS, then it's a good idea.

[BillC]

7 minutes ago, xrbrevin said:

something similar occurred with the 1200XL - the SIO port was missing its 5v connection.

i wonder if it was left out during development and they forgot to put it back before the final draft?

The stock 1200XL does have +5V connected to the SIO port, they couldn't remove it since it is also the READY signal to SIO devices, but Atari added a current limiting resistor that drops the voltage too much to be useful for most SIO powered devices.

Edited May 20, 2020 by BillC

[Daedalus2097]

Ah cool, thanks for that. If there are devices out there already that use it, it's not totally unprecedented.

[+DrVenkman]

2 hours ago, Daedalus2097 said:

Ah cool, thanks for that. If there are devices out there already that use it, it's not totally unprecedented.

With regard to the +5VDC on the SIO port are devices that use the +5V - some vintage devices like the P:R:Connection, for instance, are powered by the bus, and modern devices like an SDrive-MAX can be bus-powered as well.

 

As for the PBI, frankly there’s very little that uses it, and unless you specifically buy a device that needs it, there’s not a lot of point to doing the mod unless you’re bored on a rainy day and want to solder a wire. I have 3 800XL’s and while I’ve added the chroma line to two of them and a UAV to the other, I’ve not bothered with the PBI power mod on any of them. If I bought a Sys-Check or something that could benefit from it, I’d likely go ahead and do it, but until then I’m not going to bother. 

[Daedalus2097]

Ah yeah, I'm aware of the SIO port power alright - I had an XC12 tape deck back in the day that was bus powered, and an SD drive on there these days. Good to know there's very little PBI stuff really, sounds like quite the niche, and so the way to go I reckon would be to have a device powered from the bus with an optional 5V connection that can be taken from elsewhere if needed. Sys-Check looks like a very interesting bit of kit though - might stick that on my list for a rainy day...

 

Cheers everyone!

[TGB1718]

Not for an 800XL, but I made this for my 130XE back in the 80's

 

 

[Daedalus2097]

That's awesome  And not all that far off what I was thinking. My vague plan was an I/O board with some digital and analogue I/O stuff for simple control of random hardware, and to include some Amiga-style "clock ports". This in turn would give access to various additions like RTC modules, serial/parallel ports, I₂C bus controllers, MP3 decoders and so on. It's essentially an 8-bit CPU bus interface with a few extra control lines, so well suited to cobbling onto the PBI.

 

Anyway, it's on the long list of projects...