



      DAC12.TXT         MVS Box 850 Merrimack,NH          4/1/93




INTRODUCTION
------------

The DAC12 card is a 2 channel 12-bit Digital to Analog Converter with a
maximum sample rate of 100 khz.  Both channels have sharp cutoff low-pass
filters for signal conditioning and noise reduction.  A 5 volt precision
voltage reference is available for use with external circuitry.

The DAC12 output voltage range is -5v to +5v when the filter is bypassed. 
Voltages at the filter outputs are -10 to +10v.  These ranges can be
altered with external resistive dividers or amplifiers.  Output voltage is
determined by the value written to each channel.  The lowest value occurs
when 000h is written and the highest with FFFh.  The DACs are double
buffered so writing to the lower and upper bytes have no effect until the
Load DAC register is written to.  This way all 12 bits on both channels are
updated at once.

Dual sharp-cutoff active filters improve playback quality of stereo audio. 
They provide overshoot damping in precision servo control applications. 
The frequency rolls off at approximately 10hkz and they have a gain of 2.




SPECIFICATIONS
--------------

Block Diagram:

  PC BUS
    :                                ---- -5 to +5V DAC OUT A
    :                               :
    :   5V                 ------   :       ------    
    :  REF----------------:  DAC :  :      : FILT :
    :         :           : CH A :---------:  A   :-- -10 to +10V FILT OUT A
    :---------:-----------:      :          ------
    :         :            ------      
    :         :
    :         :                      ---- -5 to +5V DAC OUT B
    :         :                     :
    :         :            ------   :       ------    
    :          -----------:  DAC :  :      : FILT :
    :                     : CH B :---------:  B   :-- -10 to +10V FILT OUT B
    :---------------------:      :          ------
    :                      ------      
    :
                
I/O Connector pinout:                        
  1 Ground         2 NC              I/O Registers:
  3 Ground         4 NC               160h = DAC Chan A LSB (D7-0)
  5 Ground         6 DAC OUT A        161h = DAC Chan A MSB (D11-8)*
  7 Ground         8 DAC OUT B        162h = DAC Chan B LSB (D7-0)
  9 Ground        10 NC               163h = DAC Chan B MSB (D11-8)*
 11 NC            12 FILT OUT B       164H = Load DAC register
 13 NC            14 FILT OUT A      *lower 4 bits only, upper don't care
 15 NC            16 NC           
 17 NC            18 NC           
 19 NC            20 NC           
 21 NC            22 NC              Base Address Jumpers:
 23 NC            24 NC                J1 J2 J3 J4   160h= 1-5 2-6 3-7 4-8* 
 25 NC            26 10V REF OUT        o  o  o  o   1A0h= 1-6 2-5 3-7 4-8
 27 Ground        28 NC                 o  o  o  o   260h= 1-5 2-6 3-8 4-7
 29 NC            30 NC                J5 J6 J7 J8   2A0h= 1-6 2-5 3-8 4-7
 31 Ground        32 +5V OUT                         320h= 1-8 2-6 3-7 4-5
 33 -12V OUT      34 +12V OUT                                 *default

The DAC12 is often used with inexpensive PC motherboards and the MVS
ROM Drive for embedded applications or portable computers.  Using a
right angle PC Bus Expander (part number BP4) allows cards to lie down
flat.  Everything can now fit into a compact low-profile case.

The DAC12 has the same form factor as the MVS Single Board Computer. 
Corner holes are in the same position which simplifies mounting with
standoffs.  The PC Bus ends of the DAC12 and the SBC are connected with
a passive backplane.  This is constructed using 62 pin IDC connectors
(part number MVCON1) and a short length of ribbon cable.  Other PC
adapter cards can be added on in the same way.

                         LIMITED WARRANTY 

MVS will repair free of charge product suffering from manufacturing defects
for a period of 5 years after shipping.  This will be done only if it has
been determined by MVS that the product has not been misused (improper
voltages, physical alteration, etc.).  Otherwise a minimum service charge
is required.  In either case it is necessary to contact MVS for a Returned
Merchandise Authorization (RMA) number before shipping the unit.

