Kevin Hoskins Introduction Adding channels analog input/output co

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Kevin Hoskins Introduction Adding channels analog input/output co

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Micropower SO-8 Give 12-Bit Analog Interface Design Note
Kevin Hoskins
Introduction Adding channels analog input/output computer simple, inexpensive, powered compact when using LTC®1298 LTC1446 DAC. LTC1298 LTC1446 first SO-8 packaged 2-channel devices their kind. While application shown data acquisition, converters provide smallest, lowest power solutions many other analog applications. Small, Micropower LTC1298 features 12-bit ADC, 2-channel multiplexer, input S/H. Operating supply maximum conversion rate, LTC1298 draws just 340µA. built-in auto shutdown further reduces power dissipation reduced sampling rates 30µA 1ksps). serial interface allows remote operation. LTC1446 first 12-bit dual micropower SO-8 packaged DAC. features 1mV/LSB 4.095V) railto-rail output, internal 2.048V reference simple, cost-effective, 3-wire serial interface. DOUT allows cascading multiple LTC1446s without increasing number serial interconnections. Operating supply LTC1446 draws just (typ).
LTC1298 INPUT INPUT DOUT SELECT SCLK DOUT 0.1µF
2-Channel Analog Interface circuit shown Figure connects PC's serial interface using four interface lines: DTR, RTS, used transmit serial clock signal, used transfer data ADC, used receive conversion results from LTC1298, signal selects either LTC1446 LTC1298 receive input data. LTC1298's LTC1446's power dissipation allow circuit powered from serial port. lines charge capacitor through diodes LT®1021-5 regulates voltage Returning lines logic high after sending data completion conversion provides constant power LT1021-5. Using 486-33 throughput 3.3ksps LTC1298 2.2ksps LTC1446. Your mileage vary. Listing code that prompts user either read conversion result from ADC's write data word both channels.
registered trademarks Linear Technology Corporation.
74HC74 LT1021-5 47µF
150µF
LTC1446 AOUT1 AOUT2 1N914 CS/LD DOUT VOUTB VOUTA 0.1µF
74HC74
0.1µF
DN138
Figure Communicating Over Serial Port, LTC1298 LTC1446 SO-8 Create Simple, Power 2-Channel Analog Interface
09/96/138
Conclusion These SO-8 packaged data converters offer unprecedented space, power economy data acquisition system designers. They form very nice 12-bit analog interface wide variety portable, battery-powered size constrained products. They extremely easy apply require minimum passive support components interconnections.
Listing Configure Analog Interface with this Code
#define port 0x3FC/* Control register, RS232 #define inprt 0x3FE/* Status reg. RS232 #define 0x3FB/* Line Control Register #define high #define #define Clock 0x01/* #define 0x02/* #define Dout 0x10/* input #include<stdio.h> #include<dos.h> #include<conio.h> Function module sets high void set_control(int Port,char bitnum,int flag) char temp; temp inportb(Port); (flag==high) temp bitnum; output high else temp ~bitnum; output outportb(Port,temp); This function brings high (consult schematic) void CS_Control(direction) (direction) set_control(port,Clock,low);/* clock high read set_control(port,Din,low); set_control(port,Din,low);/* high make goes high else outportb(port, 0x01);/* clock Delay(10); outportb(port, 0x03);/* goes high make goes This function outputs bit(2x12) digital code LTC1446L void Din_(long code,int clock) for(x x<clock; ++x) code 1;/* align (code 0x1000000) Clock set_control(port,Din,high);/* high else set_control(port,Clock,high); Clock set_control(port,Din,low);/* set_control(port,Clock,low);/* Clock high latch
Read from Dout_() temp, volt for(x x<13; ++x) set_control(port,Clock,high); set_control(port,Clock,low); temp inportb(inprt);/* read status reg. volt 1;/* shift left serial transmission if(temp Dout) volt input high return(volt 0xfff); menu mode selection char menu() printf("Please select following:\na: ADC\nd: DAC\nq: quit\n\n"); return (getchar()); void main() long code; char mode_select; temp,volt=0; Chip select controlled RS232 line. When LCR's set, selected reverse true ADC. outportb(LCR,0x0);/* initialize outportb(LCR,0x64);/* initialize while((mode_select menu()) `q') switch(mode_select) case `a': outportb(LCR,0x0);/* selecting CS_Control(low);/* enabling Din_(0x680000, 0x5);/* channel selection volt Dout_(); outportb(LCR,0x64);/* bring high set_control(port,Din,high);/* bring signal high printf("\ncode: %d\n",volt); break; case `d': printf("Enter input code 4095):\n"); scanf("%d", &temp); code temp; code (long)temp 12;/* converting word outportb(LCR,0x64);/* selecting CS_Control(low);/* enable Din_(code,24);/* loading digital data outportb(LCR,0x0);/* bring high outportb(LCR,0x64);/* disabling set_control(port,Din,high);/* bring signal high break;
literature Data Conversion products, call 1-800-4-LINEAR. applications help, call (408) 432-1900, Ext. 2453
LT/GP 0996 155K PRINTED
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LINEAR TECHNOLOGY CORPORATION 1996

Kevin Hoskins Introduction Adding channels analog input/output co

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