Hooking an LS244 line buffer to Antic's AN0-AN2

[Rybags]

I've just soldered some wires to AN0-AN2 and next up will buffer them through a 74LS244.

 

That will have it's outputs going through a resistor ladder - a primitive way to monitor Antic's goings on via my oscilloscope.

It'll just be sitting in a protoboard outside the machine, I plan to just give it +4V and GND courtousy of a joystick port.

 

For the outputs to be enabled (ie not in high-impedence), the 1G/2G lines need to be in a low state.

 

Just tying them directly to Ground is sufficient for this? Or do I need a Resistor involved in the process?

[Bryan]

I've just soldered some wires to AN0-AN2 and next up will buffer them through a 74LS244.

 

That will have it's outputs going through a resistor ladder - a primitive way to monitor Antic's goings on via my oscilloscope.

It'll just be sitting in a protoboard outside the machine, I plan to just give it +4V and GND courtousy of a joystick port.

 

For the outputs to be enabled (ie not in high-impedence), the 1G/2G lines need to be in a low state.

 

Just tying them directly to Ground is sufficient for this? Or do I need a Resistor involved in the process?

You can just tie them to ground. You need resistors when you have conditions where power may be applied to a pin before it is applied to the IC (when multiple power supplies exist or you have connections to external devices).

[Rybags]

That's what I've done... figured worst I could do is fry the '244

 

Got it going now... just got to belt out some code for triggering the sweep when I want it.

[Bryan]

We had a situation where I work where a plug-in board was occasionally frying. It turned out that if the board wasn't seated all the way it could be powered on without the ground connection making contact. There were some pins that were used for ID purposes that were connected to ground in the connector (so the board could identify where it was plugged in) and if these ID pins were grounded but the board wasn't when power came on, the board would be toast. The ID pins became the only path to ground and too much current flowed through the ICs they were connected to. Placing inline 4.7K resistors solved the problem and the board became robust enough to survive being plugged in with the power on.

 

In a single system with a single supply, you never have to worry about power sequencing issues.

[ClausB]

monitor Antic's goings on via my oscilloscope.

Cool. Pictures yet?

[Rybags]

Pics weren't really necessary. The whole 'scope thing was necessary as it's my easiest method of measuring a 3-bit digital quantity at the ~ 1.8 MHz speeds needed.

 

I posted my findings in the Antic/GTIA internal schematics thread.

 

I had to remove the wires I soldered to the underside pins of Antic in my XEGS. I'd also put a glob of silicone hot-glue on as extra assurance and it was just too big to enable me to put the thing back together properly.

 

Since I now know the method to be "safe", in future I could probably just do it a whole lot easier with my nice socketed 800XL Antic if needed.

Edited March 22, 2009 by Rybags