1. 517212: Digital Logic Design
บทที่ 2 - หนาที่และการทำงานของวงจรดิจิทัล
12 พฤศจิกายน 2555

2. ตัวปฏิบัติการพื้นฐานทางลอจิก
ระบบดิจิทัลนั้นสรางจากพื้นฐานทางตรรกศาสตร
จอรจ บูล (George Boole) นักคณิตศาสตรชาวอังกฤษไดสรางพีชคณิต
เชิงตรรก (Boolean Algebra) ขึ้นมาในชวงทศวรรษที่ 19 ซึ่งภายหลังได
นำมาประยุกตใชในการออกแบบและสรางระบบดิจิทัล
ตัวปฏิบัติการเชิงตรรกที่ใชเปนพื้นฐานและควรทราบนั้นมีอยูเพียง 3 แบบ
ไดแก
NOT
AND
OR

3. NOT
Negation
Output is the opposite of the input, that’s all.
The symbol:
Note: There is only one input and one output for this op!

4. AND
The output will be HIGH only when all the inputs are HIGH.
The symbol:
Note: there may be more than two inputs.

5. OR
The output will be HIGH when one or more inputs are HIGH.
The symbol:

6. Basic Logic Functions
 Roadmap to what we are going to learn:
–Comparison function
–Arithmetic functions
–Code conversion function
–Encoding function
–Decoding function
–Data selection function
–Storage function
–Counting function

7. Comparison
A basic comparator compares two quantities and
indicates whether or not they are equal.
–Think about conditional statement like if or things like
that in programming.

8. Arithmetic
 Adder is the key-element circuit of
binary arithmetic.
– You can add (of course, it’s the
adder).
– You can subtract using adder with
special treatment on input number.
– You can multiply using adder with
the help of other circuits.
– You can also divide with series of
circuits in conjunction of adder.

9. Code Conversion
A code converter changes one form of coded
information into another coded form, i.e.:
–binary-to-BCD
–binary-to-Gray code
–etc.

10. Encoding and Decoding
 Encoder converts information, such as a decimal number
or an alphabetic character, into some coded form.
 Decoder does the opposite.

11. Data Selection
 Multiplexer (MUX)
– Switches digital data from several input lines on a single
output line in a special time sequence.
 Demultiplexer (DEMUX)
– Does the opposite.

12. Storage
 This function is
required in most digital
systems.
 Itcan memorize a bit of
a group of bits and
retain the information
as long as necessary.
– Flip-flops
– Registers
– etc

13. Counting
Counting is one of the most important
function in digital systems.
–Think about the loop in programming, you
cannot accomplish unless you have some
sort of counter.
To count, the counter must remember the
present numbers  it can go to the next
proper number in sequence.

18. Integrated Circuits (ICs)

19. Fixed-Function ICs
http://www.bbc.co.uk/schools/gcsebitesize/
design/images/dt_chip.jpg
http://www.dolphin.fr/corporate/announcements/
pressrelease/2002/images/dsair.jpg
http://www.tiscali.co.uk/reference/encyclopaedia/
hutchinson/images/c01356.jpg

20. Complexity Classifications for Fixed-
Function ICs
 Small-scale integration (SSI)
– Up to 10 gate circuits
 Medium-scale integration (MSI)
– 10-100 gate circuits
 Large-scale integration (LSI)
– 100-10,000 gates
 Very large-scale integration (VLSI)
– 10,000-100,000 gates
 Ultra large-scale integration (ULSI)
– More than 100,000 gates

21. Programmable Logic
 PL devices can be programmed to perform specified
logic functions using software.
–Hardware Description Language (HDL)
A design can be implemented faster and with less cost
(small volume).
 Just remember the name:
–Field Programmable Gate Array (FPGA)
–Complex Programmable Logic Device (CPLD)

22. รูป title page http://4.bp.blogspot.com/_FdGFE8NBDgc/TAdzuXy9VEI/AAAAAAAAC_A/73pzDSvpgww/s1600/mains-
frequency-monitor-circuit-diagram.jpg