Eceg 3201-dld-lec 11-registers_and_asynchoronous_counters
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This document discusses registers and counters in digital logic design. It begins by defining registers as flip-flops that store binary data and can transfer data in parallel or serial. Shift registers are introduced as registers that can shift data bit by bit. Various types of shift registers are described, including their uses in serial-parallel conversion and counting applications. Ring counters and Johnson counters are introduced as counter circuits built from shift registers. Asynchronous and synchronous counters are also discussed.
Eceg 3201-dld-lec 11-registers_and_asynchoronous_counters
- 1. Addis Ababa Institute of Technology (AAIT) Department of Electrical and Computer Engineering ECEG-3201 Digital Logic Design
- 2. AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri2 Learning Outcomes At the end of the lecture, students should get familiarized with; Registers. Counters.
- 3. 3 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Registers A flip-flop stores one bit of information. When a set of n flip-flops are used to store n bits of information, such as an n-bit number, we refer to these flip-flops as a register. Register is a digital circuit with two basic functions; data storage and data movement. A common clock is used for each flip-flop in a register. A register that provides the ability to shift its contents is called a shift register.
- 4. 4 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Registers Transmitting n bits of information at once using n separate wires is called parallel transfer. But it is also possible to transfer all bits using a single wire, by performing the transfer one bit at a time, in n consecutive clock cycles. We refer to this scheme as serial transfer.
- 5. 5 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Shift Registers A shift register is a sequential logic device made up of flip-flops that allows parallel or serial loading and serial or parallel outputs as well as shifting bit by bit. A shift register is an n-bit register with a provision for shifting its stored data by one bit position at each tick of the clock. There are different types of shift registers. Serial in Serial Out Serial in Parallel Out Parallel in Serial Out Parallel in Parallel Out
- 6. 6 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Shift Registers This sequential device loads the data present on its inputs and then moves or “shifts” it to its output once every clock cycle, hence the name “Shift register”. Common tasks of shift registers: Serial/Parallel data conversion UART (universal asynchronous receiver/transmitter) Time delay Ring counter Twisted-ring counter or Johnson counter Memory device
- 7. 7 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Characteristics of Shift Registers Number of bits (4-bit, 8-bit, etc.) Loading Serial Parallel (asynchronous or synchronous) Common modes of operation. Parallel load Shift right-serial load Shift left-serial load Hold Clear Recirculating or non-recirculating
- 8. 8 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Serial/Parallel Data Conversion 1 0 1 0 1 1 1 1Serial in Serial out Shift registers can be used to convert from serial- to-parallel or the reverse from parallel-to-serial. 1 0 1 0 1 1 1 1Serial in Parallel out 1 0 1 0 1 1 1 1 Serial out Parallel in 1 0 1 0 1 1 1 1 Parallel in Parallel out
- 9. 9 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Serial In Serial Out Shift Registers Serial-In Serial-Out (SISO) - the data is shifted serially “IN” and “OUT” of the register, one bit at a time in either a left or right direction under clock control.
- 10. 10 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Serial In Serial Out Shift Registers
- 11. 11 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Serial In Serial Out Shift Registers Clk pulse no. FF0 FF1 FF2 FF3 0 0 0 0 0 1 0 0 0 0 2 1 0 0 0 3 0 1 0 0 4 1 0 1 0 5 0 1 0 1 6 0 0 1 0 7 0 0 0 1 8 0 0 0 0 Data IN = 1010 Data OUT =00001010
- 12. 12 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Serial In Parallel Out Shift Registers
- 13. 13 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Serial In Parallel Out Shift Registers
- 14. 14 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Parallel In Serial Out Shift Registers Clk pulse no. FF0 FF1 FF2 FF3 0 0 0 0 0 1 1 0 1 0 2 0 1 0 1 3 0 0 1 0 4 0 0 0 1 5 0 0 0 0 Data IN = 1010
- 15. 15 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Parallel In Parallel Out Shift Registers
- 16. 16 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Parallel In Parallel Out Shift Registers Clk pulse no. FF0 FF1 FF2 FF3 0 0 0 0 0 1 1 0 1 0 2 0 1 0 1 3 0 0 1 0 4 0 0 0 1 5 0 0 0 0 Data IN = 1010
- 17. 17 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Universal Shift Register Universal Shift Register is a register that has both serial and parallel input and output capability. Today, there are many high speed bi-directional “universal” type Shift Registers available such as the TTL 74LS194, 74LS195,74HC194 or the CMOS 4035 which are available as 4-bit multi-function devices that can be used in either serial-to-serial, left shifting, right shifting, serial-to-parallel, parallel-to-serial, or as a parallel-to-parallel multifunction data register, hence the name “Universal”.
- 18. 18 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Universal Shift Register Universal shift registers are very useful digital devices. They are frequently used in arithmetic operations to shift data to the left or right for multiplication or division.
- 19. 19 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Shift Register based Counters A shift register counter is basically a shift register with the serial output connected to the serial input to produce a special sequence. There are two basic types of counters which are based on shift registers Ring counters Johnson counters
- 20. 20 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Ring Counters In a ring counter the output of the most significant stage is fed back to the input of the least significant stage. E.g. 4 bit ring counter
- 21. 21 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 4 bit Ring Counters It got only 4 distinct states, hence mod-4 counter. Only 4 of the maximum 16 states are used, making ring counters very inefficient in terms of state usage. But the major advantage of a ring counter over a binary counter is that it is self-decoding. No extra decoding circuit is needed to determine what state the counter is in.
- 22. 22 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 5 bit Ring Counters
- 23. 23 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 10 bit Ring Counters
- 24. 24 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Johnson Counters Johnson counters are a variation of standard ring counters, with the inverted output of the last stage fed back to the input of the first stage. They are also known as twisted ring counters. An n-stage Johnson counter yields a count sequence of length 2n modulus, so it may be considered to be a mod-2n counter. E.g. 4 bit and 5 bit Johnson counters
- 25. 25 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 4 bit Johnson Counter
- 26. 26 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 4 bit Johnson Counter
- 27. 27 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 5 bit Johnson Counter
- 28. 28 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 5 bit Johnson Counter
- 29. 29 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Counters There are two basic types of counters Asynchronous counters Synchronous counters
- 30. 30 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Asynchronous counters Counters that do not have a fixed time relationship with each other and generally do not count at the same time. An asynchronous counter is one in which the flip-flops within it do not change states at exactly the same time because they do not have a common clock pulse. Also known as ripple counters.
- 31. 31 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 2-Bit Asynchronous Binary Counter
- 32. 32 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 3-Bit Asynchronous Binary Counter
- 33. 33 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 4-Bit Asynchronous Binary Counter
- 34. 34 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Synchronous Counter The counter have a fixed time relationship with each other and generally count at the same time. A synchronous counter is one which all the flip-flops are connected to the same clock.
- 35. 35 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 2-Bit Synchronous Counter
- 36. 36 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 3-Bit Synchronous Counter
- 37. 37 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri 4-Bit Synchronous Counter
- 38. 38 AAIT, Department of Electrical and Computer Engineering Nebyu Yonas Sutri Reading assignment. Read about synchronous counters design, on Fundamentals of digital logic with verilog design, Section 8.7, page 495-505. What to Do this Week?