Sio ready/motor control current draw

[foft]

What is the peak current draw allowed from ready and motor control on the sio port? The 1010 seems to take a fair bit from motor control and I guess the XC12 takes more - since it has no psu. Are there other more power hungry devices?

[kskunk]

Except for the 1200XL, +5V/READY is wired directly to 5V power. Motor control is designed to switch up to 500mA. (The 1200XL is different - limited to only a few milliamps on the 5V/READY line - leading some 1200XL owners to mod for full power.)

 

The practical limit is determined by the Atari's PSU and all the peripherals, cartridges, mods, and expansions that you're sharing with. On an XL/XE, you can plug in a beefier external supply and draw quite a lot on SIO, but on the 800/400, the internal supply is the limiting factor.

 

I've seen 100mA mentioned - I don't know if that's the official recommendation.

 

- KS

[+bob1200xl]

The official current limit is 50ma. They put a 100 ohm resistor in series with the +5v supply on the 1200XL, which would source 50ma into a 0 ohm load - not quite the same as a useful 50ma limit. (what were those guys thinking?)

 

The power supplies in most of the XLs are current limited as well as thermally protected. (this may not apply to some of the cheaper external 'bricks'). Not a good plan to cook your power supplies by hanging a lot of extra load on them, however. Get rid of the resistor in the 1200XLs, but keep close to the 50ma limit.

[ricortes]

Haven't thought about this in years. IIRC

The PR:Connection was SIO READY<?> powered. Someone posted some pics here http://www.flickr.com/photos/jerryc98/8127843661/

There was also the XM301 modem.

The PR was a 6502 type microcontroller and I think the XM301 was an 8051 type device. I can't imagine them not drawing at least a couple of hundred mamps.

 

Something you didn't ask but I have been following your project with great interest. The joystick ports are also supposed to supply 5V. I believe there is a low spec on it, like 50 mamp, but seem to recall some devices drew up to 200 mamps.

 

Ultimately the amount of power would be limited by the power supply and circuits on board the MB. The XL/XE computers typically draw 1-1.2 amps and came with power supplies in the range of 1.1 to 1.5 amps. The 1200XL that Bob mentioned came with a ~31 Watt AC power supply and had to use two 7805s/paths on the MB to get enough current to supply the chips.

 

So in practice, people did exceed the specs, even Atari Corporation. No one exceeded it by a huge amount because you couldn't.<sic>

Edited October 5, 2013 by ricortes

[foft]

Thanks. Very helpful to know. Might need an option of an external psu for my project, though I imagine most devices will be fine. I'll use a suitably rated transistor for 500mA on motor control.

 

Since the joystick ports were mentioned, all the inductors - I'm not sure what they are for! To provide protection against rapid current surges on connecting a device?