Interfacing with peripherals: analog to digital converters and digital to analog converters in 8086 (MCMP)
1. UJJAIN ENGINEERING COLLEGE, UJJAIN
DEPARTMENT OF ELECTRONICS AND
COMMUNICATION ENGINEERING
TOPIC -: INTERFACING WITH PERIPHERALS- ANALOG
TO DIGITAL CONVERTERS AND DIGITAL TO ANALOG
CONVERTERS IN 8086
GUIDED BY :- MISS ANSHUL MALIK
PRASANNA VYAS (0701ec191043)
PRASHANT KAUSHAL (0701ec191044)
PRIYASH KIRADE (0701ec191045)
RADHESHYAM PARMAR (0701ec191046)
RAHUL JARIWALA (0701ec191047)
NIMESH SINGH (0701ec191037)
NISHA MAHESHWARI (0701ec191038)
PALAK GUPTA (0701ec191039)
PANKHURI VAPTA (0701ec191040)
PARTH ARJARIYA (0701ec191041)
PRANITA NIRAPURE (0701ec191042)
Submitted By :-
2. SYNOPSIS
• Interfacing with peripherals, 8255 PPI in brief
• ADC interfacing
• ADC 0808/0809
• Interfacing ADC 0808 with 8086 using 8255 PPI
• DAC interfacing
• AD 7523 8 bit multiplying DAC
• Interfacing AD 7523 with 8086 using 8255 PPI
3. INTERFACING WITH PERIPHERALS
• Any application of a microprocessor based system requires the
transfer of data between external circuitry to the microprocessor and
from microprocessor to the external circuitry. The transfer of data is
called input/output data transfer or I/O data transfer. This data
transfer is done with the help of I/O ports.
• This type of interfacing is called I/O interfacing. External devices
(connected to I/O ports) used to interface are called peripheral
devices.
• There are many peripheral devices which can be interfaced with
microprocessor like keyboard, mouse, printer, 8253 timer, 8255 PPI,
ADCs and DACs.
4. 8255 PROGRAMMABLE PERIPHERAL
INTERFACE(PPI)
For most of the applications 8086 needs parallel input ,output data
to/from the peripherals.
8255 is a device used to interface different real time peripherals to
the microprocessors which can be initialized for different modes
operations like simple I/O, Strobed I/O and handshaking I/O.
It has three 8-bit parallel ports : port A, port B, port C.
6. MODES OF OPERATION
8255 can be used in two modes: Bit set/Reset (BSR) mode and I/O
mode. The BSR mode is used to set or reset the bits in port C.
The I/O mode is further divided into 3 modes: mode 0, mode 1
and mode 2.
• Mode 0:
Ports A, B, and C can be individually programmed as input or output
ports.
Port C is divided into two 4-bit ports which are independent from
each other.
7. MODES OF OPERATION
• Mode 1:
Ports A and B are
programmed as input or
output ports.
Port C is used for
handshaking. In the
handshake mode, two types
of I/O data transfer can be
implemented: status check
and interrupt.
• Mode 2:
Port A is programmed to be
bi-directional.
Port C is for handshaking.
Port B can be either input or
output in mode 0 or mode 1.
8. ADC INTERFACING
This topic is aimed at the study of 8-bit and 12-bit analog
to digital converters and their interfacing with 8086. In
most of the cases, the PIO 8255 is used for interfacing the
analog to digital converters with a microprocessor.
• The function of an A/D converter is to produce a digital word
which represents the magnitude of some analog voltage or
current.
9. ADC INTERFACING
• The resolution of an A/D converter refers to the number of bits
in the output binary word.
• Accuracy and linearity specifications have the same meaning
for an A/D converter as they do for a D/A converter.
• Another important specification for an ADC is its conversion
time.
10. ADC INTERFACING
• This is simply the time it takes the converter to produce a valid output binary
code for an applied input voltage.
• After the conversion is over, the ADC sends end of conversion (EOC) signal to
inform the microprocessor and the result is ready at the output buffer of the
ADC.
• The time taken by the ADC from the active edge of SOC pulse (the edge at
which the conversion process actually starts) till the active edge of EOC signal is
called as the conversion delay of the ADC.
11. ADC INTERFACING
• The available ADCs in the market use different conversion
techniques for the conversion of analog signals to digital
signals.
• Parallel converter or flash converter, Successive approximation
and dual slope integration techniques are the most popular
techniques used in the integrated ADC chips.
12. ADC 0808/0809
• These are unipolar analog to digital converters, i.e. they are able to convert
only positive analog input voltages to their digital equivalents.
• These chips do not contain any internal sample and hold circuit.
• The analog to digital converter chips 0808 and 0809 are 8-bit CMOS,
successive approximation converters.
• The conversion delay is 100 µs at a clock frequency of 640 kHz, which is
quite low as compared to other converters.
13. ADC 0808/0809
• These converters internally have a
3:8 analog multiplexer so that at a
time eight different analog inputs
can be connected to the chips.
• Out of these eight inputs only one
can be selected for conversion by
using address lines ADD A, ADD B
and ADD C, as shown.
• Using these address inputs,
multichannel data acquisition
systems can be designed using a
single ADC.
15. ADC INTERFACING
• A general algorithm for ADC interfacing contains the following
steps :
1. Ensure the stability of analog input, applied to the ADC.
2. Issue start of conversion (SOC) pulse to ADC.
3. Read end of conversion (EOC) signal to mark the end of
conversion process.
4. Read digital data output of the ADC as equivalent digital output.
17. INTERFACING ADC 0808 WITH
8086 USING 8255 PORTS
Interface ADC 0808 with 8086 using 8255 ports. Use Port A of
8255 for transferring digital data output of ADC to the CPU and
Port C for control signals. Assume that an analog input is present
at I/P2 of the ADC and a clock input of suitable frequency is
available for ADC. Draw the schematic and write required ALP.
18. INTERFACING ADC 0808 WITH
8086 USING 8255-STEPS
• The analog input I/P2 is used & therefore address pins A,B,C should
be 0,1,0 respectively to select I/P2.
• The OE (Out put latch Enable) & ALE pins are already kept at +5v to
select the ADC and enable the outputs.
• Port C upper acts as the input port to receive the EOC signal while
Port C lower acts as the output port to send SOC to ADC.
• Port A acts as a 8-bit input data port to receive the digital data
output from the ADC.
19. INTERFACING ADC 0808 WITH
8086 USING 8255
• The 8255 control word is written as
follows:
D7 D6 D5 D4 D3 D2 D1 D0 Control
Word
1 0 0 1 1 0 0 0 = 98H
21. INTERFACING ADC 0808 WITH
8086 USING 8255 PORTS- ALP
• The required
ALP is given as
follows:
22. DAC INTERFACING
The digital to analog converters convert binary numbers into
their analog equivalent voltages or currents.
• Several techniques are employed for digital to analog
conversion.
i. Weighted resistor network
ii. R-2R ladder network
23. DAC INTERFACING
• The DAC find applications in areas like :
1. Digitally controlled gains
2. Motor speed controls
3. Programmable gain amplifiers etc.
• D/A converter have many applications besides those where they are used with
a microcomputer. Most speech synthesizer integrated circuits contain a D/A
converter to convert stored binary data words into analog audio signals.
24. DAC INTERFACING
Characteristics:
1. Resolution: It is a change in analog output for one LSB change
in digital input. It is given by(1/2^n )*Vref.
2. Settling time: It is the time required for the DAC to settle for a
full scale code change
25. AD 7523 8-BIT MULTIPLYING DAC
• Intersil’s AD 7523 is a 16 pin DIP, multiplying digital to analog
converter, containing R-2R ladder (R=10K) for digital to analog
conversion.
• Power supply +5v to +15v
• Vref -> -10v to +10v
• The maximum analog output voltage will be +10v
26. AD 7523 8-BIT MULTIPLYING DAC
• A Zener is connected between OUT1 & OUT2 to save the DAC from
negative transients.
• An operational amplifier is used as a current – to – voltage converter
at the output of AD 7523.
• An external feedback resister acts to control the gain.
28. INTERFACING OF AD 7523 WITH 8086
Interface DAC AD7523 with the 8086
running at 8MHz & write ALP to generate a
saw tooth waveform of period 1ms with
Vmax 5v.
