

      DAC8SPEC.TXT  8 BIT DIGITAL TO ANALOG COVERTER
      ----------------------------------------------


The DAC8 card is a 2 channel 8-bit Multiplying Digital to Analog Converter. 
Typical applications include servo, programmable power supply, sound card,
variable gain amplifier, etc..  Maximum sample rate is 44 khz.  Both
channels have sharp cutoff low-pass filters for signal conditioning and
noise reduction.  A 2.5 volt voltage reference is available for use with
external circuitry.

The voltage range is 0 to -2.5v when DAC outputs are used directly (filter
bypassed).  When filter outputs are used voltage will be 0 to 5v.  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 00h is written and the highest with FFh.

Dual sharp-cutoff active filters improve playback quality of stereo audio
and provide overshoot damping in control applications.  The cutoff
frequency is approximately 4hkz and they have a gain of 2.

These filters can be used independently from the DAC circuit.  This means
they can be used to improve record quality when switched to ADC inputs if
one is installed.  A single filter with extremely sharp cutoff and a gain
of 4 can be implemented by placing the two filters in tandem.  External
electrolytic capacitors might be used on the filter inputs to decouple DC
offsets.




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

Resolution: 0.39% Full Scale 
Filter output impedance: 220ohm (drives speaker/phones 60 ohms or greater)

Block Diagram:

 PC BUS
  :                  ,--DAC A IN   ,----0 to -2.5V DAC A OUT
  :  ,----,          :             :
  :  :2.5v;  J11 J16 :  ,------,   :          ,------,   
  :  :VREF;---o---o-----:  DAC :   : J9 J10   : FILT :
  :  '----' :           : CH A :-----o--o-----:  A   :---0 to 5V FILT A OUT
  :-------- : ----------:      :           :  '------'
  :         :           '------'           :
  :         :                              '--------- FILT A IN
  :         :
  :         :        ,---DAC B IN  ,---0 to -2.5V DAC B OUT
  :         :        :             :
  :         :  J12   :  ,------,   :          ,------,
  :         '---o-------:  DAC :   : J14 J15  : FILT :
  :                     : CH B :-----o--o-----:  B   :---0 to 5V FILT B OUT
  :---------------------:      :           :  '------'
  :                     '------'           :
  :                                        '--------- FILT B IN


I/O Connector pinout:                        
  1 Ground         2 DAC A in     
  3 Ground         4 DAC B in     
  5 Ground         6 DAC A out           Registers:
  7 Ground         8 DAC B out            DAC Chan A (out) = 262h*
  9 Ground        10 Filter A in          DAC Chan B (out) = 263h*
 11 Filter B in   12 Filter A out 
 13 Filter B out  14 NC           
 15 NC            16 NC           
 17 NC            18 NC           
 19 NC            20 NC           
 21 NC            22 NC             Address Jumpers:
 23 NC            24 NC              J1 J2 J3 J4  162-163=1-5 2-6 3-7 4-8
 25 Ground        26 NC               o  o  o  o  1A2-1A3=1-6 2-5 3-7 4-8
 27 Ground        28 +5v out          o  o  o  o  262-263=1-5 2-6 3-8 4-7*
 29 Ground        30 +2.5 vref out   J5 J6 J7 J8  2A2-2A3=1-6 2-5 3-8 4-7
 31 Ground        32 -12v out                     322-323=1-8 2-6 3-7 4-5
 33 Ground        34 +12v out                                 *default




The DAC8 is often used with inexpensive PC motherboards and the MVS ROM
Drive for embedded applications or portable computers.  Using a right angle
Passive Backplane (part number PB4) allows the cards to lie down flat. 
Everything can now fit into a compact low-profile case.

The DAC8 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 DAC8 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.

