Electronic Components Datasheet Search |
|
ADC0801LJ Datasheet(PDF) 33 Page - National Semiconductor (TI) |
|
|
ADC0801LJ Datasheet(HTML) 33 Page - National Semiconductor (TI) |
33 / 41 page Functional Description (Continued) Note 25: In order for the microprocessor to service subroutines and interrupts, the stack pointer must be dimensioned in the user’s program. For amplification of DC input signals, a major system error is the input offset voltage of the amplifiers used for the preamp. Figure 18 is a gain of 100 differential preamp whose offset voltage errors will be cancelled by a zeroing subroutine which is performed by the INS8080A microprocessor sys- tem. The total allowable input offset voltage error for this preamp is only 50 µV for 1⁄4 LSB error. This would obviously require very precise amplifiers. The expression for the differ- ential output voltage of the preamp is: where I X is the current through resistor RX. All of the offset error terms can be cancelled by making ±I XRX= VOS1 + V OS3 −V OS2. This is the principle of this auto-zeroing scheme. The INS8080A uses the 3 I/O ports of an INS8255 Program- able Peripheral Interface (PPI) to control the auto zeroing and input data from the ADC0801 as shown in Figure 19. The PPI is programmed for basic I/O operation (mode 0) with Port A being an input port and Ports B and C being output ports. Two bits of Port C are used to alternately open or close the 2 switches at the input of the preamp. Switch SW1 is closed to force the preamp’s differential input to be zero dur- ing the zeroing subroutine and then opened and SW2 is then closed for conversion of the actual differential input signal. Using 2 switches in this manner eliminates concern for the ON resistance of the switches as they must conduct only the input bias current of the input amplifiers. Output Port B is used as a successive approximation regis- ter by the 8080 and the binary scaled resistors in series with each output bit create a D/A converter. During the zeroing subroutine, the voltage at V x increases or decreases as re- quired to make the differential output voltage equal to zero. This is accomplished by ensuring that the voltage at the out- put of A1 is approximately 2.5V so that a logic “1” (5V) on SAMPLE PROGRAM FOR Figure 17 INTERFACING MULTIPLE A/D’s IN AN MC6800 SYSTEM DS005671-A3 SAMPLE PROGRAM FOR Figure 17 INTERFACING MULTIPLE A/D’s IN AN MC6800 SYSTEM DS005671-A4 www.national.com 33 |
Similar Part No. - ADC0801LJ |
|
Similar Description - ADC0801LJ |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |