



      ADDAC16.TXT         MVS Box 850 Merrimack,NH          3/20/94




HARDWARE
--------

The ADDAC16 card is a 24 channel 16-bit Successive Approximation type
Analog to Digital Converter and single channel 16-bit Digital to Analog
Converter.  Maximum sample rate is 50 khz.  The first two ADC channels
(ADCIN0-1) have low-pass filters for signal conditioning and noise
reduction.  A 2.5 volt precision voltage reference is available for use
with external circuitry.  A TTL compatible output bit is provided for
control of a relay, an indicator, or any other 0-5v device.

The ADDAC16 in ADC mode has single ended inputs with a voltage range of
-2.5 to +2.5v.  Voltages exceeding -5.0 to +5.0 volts will damage the
device.  Higher voltages can be read with the use of external resistive
dividers as long as the voltages applied to the ADC inputs are within the
operational range.  For example two 10k resistors can be connected to the
input resulting in an input range of 5v.  A 1k and a 10k can be used for a
25v range.  Ten-turn variable resistors would allow precision adjustment.

Low voltage devices such as a microphone, pressure sensor, or thermocouple
can be read if external amplification is used.  Ground, +5 volts, +12
volts, and -12 volts are available at the I/O connector for powering remote
circuitry.  The amplifiers should be physically located near the sensors. 
It is not practical to put amplifiers for remote sensors near the converter
due to noise problems.

24 channels are implemented with an analog switch type multiplexer.  Single
pole lo-pass filters on channels 0-1 improve record quality in stereo audio
applications and allow longer cables when used for data logging.  The
roll-off frequency is approximately 22khz.




SOFTWARE
--------

ADC mode is selected when 1 is written to bit 7 of the Control Register. 
Analog to Digital conversion is started by writing to the Converter
Address.  The value of the byte written is not important.  The sample value
is read from the same address no sooner than 20 microseconds later.  The
data can be read as a 16 bit value or as two separate 8 bit bytes (MSB and
LSB).  +2.5 volts reads as 7FFFh, 0 volts reads as 0000h, and -2.5 volts
reads as 8001h.

Channels are selected by writing to the lower six bits of the Control
Register.  Bits 0-2 control the 8:1 multiplexer channels and bits 3-5 are
multiplexer inhibit signals.  98h-9Fh select channels 0-7, A8h-AFh select
channels 8-15, and B0h-B7h select channels 16-23.  It is advisable to wait
a few microseconds for the multiplexer to stabilize before starting
conversion.

DAC mode is enabled while Control Register bit 7 is 0.  D to A conversion
is initiated by writing to the upper byte of the Converter Address. 
Writing to the lower byte alone will have no effect on the output voltage.

In both ADC and DAC modes it is possible to initiate the next conversion
before the current conversion is complete.  This allows for minimum delay
between conversion cycles.  A TTL output is also available as bit 6 of the
Control Register.  This register also contains the multiplexer channel
selection so remember to properly mask the bits when doing both operations
at once.

Source code for the demo programs is included showing how to use the
ADDAC16 with BASIC, Assembly Language, or C.  The ADC demos continually
display the input voltage at all 24 channels as hex words.  DAC demos
generate a ramp on the DACOUT pin.  The code can be run on a PC or the MVS
Single Board Computer with proper modification.  ADC16SBC.C is a program
for the SBC that uses the LED instead of a VGA screen to display readings. 
Read the source code files for more detailed information.

A version is available at no extra cost (ADDAC16b) that has 8 pairs of
differential inputs instead of the 24 single ended.  ADC0-7 are inverting
inputs and are connected to the signal side of twisted pair or center of a
coaxial cable.  ADC16-23 are non-inverting inputs.  Noise, which appears as
a common mode signal (same phase on both wires), is nulled out by the
differential input amplifier.

SCALE and OFFSET adjustments are provided which allow operation with inputs
of 0-5v, +-5v, and +-2.5v.  Turning SCALE counter-clockwise reduces gain
and allows the ADC to read higher voltages.  Turning OFFSET
counter-clockwise brings the input to the ADC section more negative
(opposite of multiplexer inputs).  Factory default setting are for gain of
1 no offset (-2.5 volts reads as 7FFFh, 0 volts reads as 0000h, and +2.5
volts reads as 8001h).




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

Size: 3.2"x4.2"x0.5"  
Temp: -20 to 70C   
Supply Voltage: 4.8-5.5v,+-11 to 13v
Humidity: 0-95 percent non-condensing    
Vibration: 10-60Hz 2mm pp


Block Diagram:
                                                       PC BUS
                                 ,-------,    ,-----,    :   ,-----,
         ,------,  ,------------>:       :    :     :    :---: DAC :
         : FILT :  : ,---------->:       :--->: ADC :----:   :     :-->DACOUT
ADCIN0-->:  0   :--' : ADCIN2--->:  24   :    :     :    :   '-----'
         :      :    : ADCIN3--->: (8x3) :    '-----'    :       ^
         '------'    : ADCIN4--->: CHAN  :       ^       :       :
                     : ADCIN5--->:  MPX  :       :       :       :
         ,------,    : ADCIN6--->:       :   ,------,    :       :
         : FILT :    : ADCIN7--->:       :   : VREF :------------'
ADCIN1-->:  1   :----' ADCIN8--->:       :   '------'    :
         :      :                :-------:               :
         :      :      ADCIN9--->:       :               :
         '------'     ADCIN10--->:       :       ,----------,
                      ADCIN11--->:       :       :          :-->TTLOUT
                      ADCIN12--->:       :<------: CONTROL  :
                      ADCIN13--->:       :       : REGISTER :
                      ADCIN14--->:       :       :          :
                      ADCIN15--->:       :       '----------'
                                 :-------:
                      ADCIN16--->:       :
                      ADCIN17--->:       :
                      ADCIN18--->:       :
                      ADCIN19--->:       :
                      ADCIN20--->:       :
                      ADCIN21--->:       :
                      ADCIN22--->:       :
                      ADCIN23--->:       :
                                 '-------'


I/O Connector pinout:
                                       ADC/DAC Registers:
  1 Ground         2 ADCIN2      
  3 ADCIN4         4 ADCIN1           Converter LSB    = 260h    
  5 ADCIN6         6 ADCIN0           Converter MSB    = 261h
  7 ADCIN7         8 ADCIN3           Control Register = 264h:
  9 ADCIN5        10 ADCIN10            D0=MPX Bit 0   D4=INH 8-15  
 11 ADCIN12       12 ADCIN9             D1=MPX Bit 1   D5=INH 0-7   
 13 ADCIN14       14 ADCIN8             D2=MPX Bit 2   D6=TTLOUT
 15 ADCIN15       16 ADCIN11            D3=INH 16-23   D7=MODE (DAC=0 ADC=1)
 17 ADCIN13       18 ADCIN18     
 19 ADCIN20       20 ADCIN17      
 21 ADCIN22       22 ADCIN16           I/O Address Jumpers:
 23 ADCIN23       24 ADCIN19      
 25 ADCIN21       26 Ground           160-17Fh = J1-J5 2-6 3-7 4-8
 27 DACOUT        28 Ground           1A0-1BFh = 1-6 2-5 3-7 4-8
 29 VREF 2.5v     30 Ground           260-27Fh = 1-5 2-6 3-8 4-7 (default)
 31 TTLOUT        32 +5v out          2A0-2BFh = 1-6 2-5 3-8 4-7
 33 -12v out      34 +12v out         320-33Fh = 1-8 2-6 3-7 4-5


Mounting:
                                   
The ADDAC16 is often used with inexpensive PC motherboards and an 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 in a compact low-profile case.

The ADDAC16 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 end of the ADDAC16 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.

