I'm a novice when it come to electrical engineering and I may be missing a few key concepts but I'll try my best to respond to questions.

I have a "Low Cost 10-Bit Monolothic D/A Converter" (AD561J) that is in an arcade unit. I am attempting to inspect the data coming into the DAC using a logic analyzer with 8 leads. I'll have to do this for another DAC on the board which has an identical configuration.

What is the best way to convert these 10-bits that come in at the same time into a binary stream that I can then inspect with my logic analyzer?

DACY# correspond to the input pins. For example:

 DACY1 - 0
 DACY2 - 1
 DACY3 - 1
 DACY4 - 0
 DACY5 - 1
 DACY6 - 0
 DACY7 - 1
 DACY8 - 0
 DACY9 - 1
DACY10 - 1

And the output:


Preferably as soon as all 10 inputs have been received. Looking at the datasheet for the DAC I don't see a clock input. How does the DAC know when to output the correct voltage, or is it always fluctuating as new bits come down the pipe?

Bottom line: How can I turn 10 digital inputs into one binary output, preserving the bit significance order?

Any help would be greatly appreciated!

  • 1
    \$\begingroup\$ It would be best to measure them with a multi-channel logic analyzer. Otherwise you'll have to sample them with a sufficiently fast clock and a multiplexor to send each in turn - and yes, you will have to do something to reliably establish the framing. A possibly practical alternative would be to look at the analog output with a scope. \$\endgroup\$ – Chris Stratton Mar 17 '13 at 0:33
  • \$\begingroup\$ Sorry if I wasn't clear. I have a 8 channel logic analyzer from Saleae. he problem is I've got 20 points I need to observe. I've looked at the output with a scope, but part of the project I'm working on is that I need to interpret and respond to that data on a PC. Processing 20 points as a high frequency will be VERY CPU intensive. It would be much more efficient to view 3 channels (X, Y, Z) and obtain exactly the same data. \$\endgroup\$ – Caesar Kabalan Mar 17 '13 at 1:01
  • \$\begingroup\$ No, it won't. To capture 10 multiplexed bits of information on a single channel, you will have to multiplex and sample at least 10 times as fast as you would when using 10 channels, generating just as much data and approximately the same computational load. You might be able to learn quite a bit by only capturing a few of the more significant bits though. Your first task, really, will be to determine what the update rate even is, using a sufficiently fast scope or by watching a handful of bits with an oversampling logic analyzer and seeing how often any of them change. \$\endgroup\$ – Chris Stratton Mar 17 '13 at 1:26
  • \$\begingroup\$ Is this one of those arcade games that has a vector display rather than a raster display? Or is the DAC being used to produce audio? \$\endgroup\$ – Dave Tweed Mar 17 '13 at 2:17
  • \$\begingroup\$ Chris, I see what you mean. I'm going to do some testing and see just how granular I really need to be. It's a vector display that supports ~1000 rows/columns. I may be able to get away with 8 inputs or less. still gives me 99.2% accuracy if my math is right. 8 bits instead of 10. \$\endgroup\$ – Caesar Kabalan Mar 17 '13 at 3:42

To answer one of your questions, this DAC (I've added a link to your question) has no internal register, so yes, it is constantly converting whatever 10-bit value that appears on its inputs to the corresponding analog value.

| improve this answer | |

I've investigated the issue more and I've decided to get the information that went to the DAC from elsewhere. The basic jist is that the data that goes to the screen of an arcade game goes to a DAC. I've decided to see if I can watch the RAM of the game to look at the draw commands.

For a more detailed look at my analysis, check here: http://wiki.spectralcoding.com/project:atari_asteroids_autoplay?&#pm2

| improve this answer | |
  • \$\begingroup\$ Looking at the schematics for the game provided in your link, you'll see that there is a sample-hold circuit at the output of each DAC that is updating at 3 MHz, so this defines your data rate. But wouldn't it be more in the spirit of a game-playing robot to use a video camera pointed at the games's actual screen, rather than tapping into the circuitry of the game itself? \$\endgroup\$ – Dave Tweed Mar 17 '13 at 14:14

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