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.