Re: Help ID card please

[Rubywand <rubywand@swbell.net>]

Richard Hall writes ...
> 
> Anybody know how to access this DAC card? Can I assume it be accessed from
> basic?
> 
> Thanks
> Richard Hall
> 
> http://www.richard.hall.net/daccard.jpg
> 
> Apple II educational software http://members.xoom.com/AV_Systems


     Your card scan is very clear. The card is not one I recognize. It seems
to be a way to create sound output based upon byte values sent to the card.
There is a "SPK" output to directly drive a speaker and an "AUX" output which
seems to be a 'line level' output intended for connecting to a hi-fi
amplifier.

     Evidently, frequency of your output depends entirely upon how rapidly
you write to the card. Ampltude of output at any given moment would depend
upon the value written. The volume of the speaker output is, probably,
controled by the slide pot located near the 'power amp' IC.

     So, the card would work for producing sound effects, musical tones, and
speech.

     You should be able to use the DAC card in a somewhat limited way from
BASIC. Probably, you just POKE the amplitude value at a Slot I/O address--
like, if the card is in Slot 4, you could POKE values at 49344 ($C0C0 in
hex). For example:

50 POKE 49344,13

The base I/O address for a Slot is $C0n0-- n= Slot number + 8. (If the card
were in Slot 7, you would POKE to 49392, which is $C0F0 in hex.)


     A quick way to check the above ideas is (with power OFF) to plug the
card into Slot 4 and connect a speaker to the SPK output using a hi-fi cable
and/or clips (or connect a hi-fi cable from AUX to a stereo amp input). Set
the card volume control (maybe) to about the middle position.

     Then, turn ON your computer and enter this short program:

3 A=49344
5 FOR I=5TO15 STEP5: POKE A,I: NEXT I: GOTO 5

     You may need to adjust the 'volume control upward to hear the tone
(which, I guess, will mainly be a low frequency sawtooth.)  If you get a tone
you are probably on the right track. (Do a RESET to stop the program.)

     You can experiment to determine how many bits are actually used to set
amplitude. Probably it's either 4 bits (POKE values 0-15) or 8 bits (POKE
values 0-255).

     If 8 bits is right, a better tone test (one spanning a wider amplitude
range) would be

3 A=49344
5 FOR I=63TO255 STEP96: POKE A,I: NEXT I: GOTO 5


     Since the card expects software to construct the output waveform, BASIC
is too slow to do much with the card. Instead, you would have a set of tables
in memory. A machine code routine would create a sound by reading a table and
sending the values to the card. This would let you create a wide range of
sounds.

     A BASIC program could BLOAD the tables and output routine and use CALLs
to play selected effects, musical tones, or speech.



Rubywand