Digital Electronics

Discussion in 'Homework Help' started by krishnapriya234, Mar 2, 2011.

  1. krishnapriya234

    Thread Starter New Member

    Mar 2, 2011
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    I need help for the following questions as i am unable to answer them properly.


    1. What test equipment can be used to troubleshoot for 7474 shift register circuit?

    2. List the five modes of operation for the 74194 universal shift register IC.

    3. List several uses of shift registers in digital systems.
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Make an effort, tell us what you think the answers are.
     
  3. krishnapriya234

    Thread Starter New Member

    Mar 2, 2011
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    2. List the five modes of operation for the 74194 universal shift register IC.


    The five modes of operation for the 74194 universal shift register IC are
    a. Reset ( clear )
    b. Shift – Left
    c. Shift – Right
    d. Parallel Load
    e. Hold ( Do Nothing)


    3. List several uses of shift registers in digital systems.

    One of the most common uses of a shift register is to convert between serial and parallel interfaces. This is useful as many circuits work on groups of bits in parallel, but serial interfaces are simpler to construct. Shift registers can be used as simple delay circuits. Several bidirectional shift registers could also be connected in parallel for a hardware implementation of a stack.
    SIPO registers are commonly attached to the output of microprocessors when more output pins are required than are available. This allows several binary devices to be controlled using only two or three pins - the devices in question are attached to the parallel outputs of the shift register, then the desired state of all those devices can be sent out of the microprocessor using a single serial connection. Similarly, PISO configurations are commonly used to add more binary inputs to a microprocessor than are available - each binary input (i.e. a switch or button, or more complicated circuitry designed to output high when active) is attached to a parallel input if the shift register, then the data is sent back via serial to the microprocessor using several fewer lines than originally required.
    Shift registers can be used also as pulse extenders. Compared to monostable multivibrators, the timing has no dependency on component values, however it requires external clock and the timing accuracy is limited by a granularity of this clock. Example: Ronja Twister, where five 74164 shift registers create the core of the timing logic this way (schematic).
    In early computers, shift registers were used to handle data processing: two numbers to be added were stored in two shift registers and clocked out into an arithmetic and logic unit (ALU) with the result being fed back to the input of one of the shift registers (the accumulator) which was one bit longer since binary addition can only result in an answer that is the same size or one bit longer.
    Many computer languages include instructions to 'shift right' and 'shift left' the data in a register, effectively dividing by two or multiplying by two for each place shifted.
    Very large serial-in serial-out shift registers (thousands of bits in size) were used in a similar manner to the earlier delay line memory in some devices built in the early 1970s. Such memories were sometimes called circulating memory. For example, the DataPoint 3300 terminal stored its display of 25 rows of 72 columns of upper-case characters using fifty-four 200-bit shift registers, arranged in six tracks of nine packs each, providing storage for 1800 six-bit characters. The shift register design meant that scrolling the terminal display could be accomplished by simply pausing the display output to skip one line of characters.

    1. What test equipment can be used to troubleshoot for 7474 shift register circuit?

    I have no clue for this answer.please kindly help me.
     
  4. mjhilger

    Member

    Feb 28, 2011
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    This may be too late, but you list a 7474 is a shift register. A 7474 is in fact a D flip flop - several may be strung together to form a shift register, but by it self it just registers 1 bit.
    As for testing, think about the inputs and outputs and what type of failure modes you expect. How would you check for each failure mode (don't immediately think about test equipment at first, just identify what signals you would like to look at and how many to determine if that failure is occuring or not). Once you have that thought try to look at your available test equipment to determine what would allow you to make the verifications you thought about. For instance one failure mode could be that you suspect the clear (reset) is stuck and not allowing anything other than clear (0) output. A handheld logic probe checks for glitches and shows on an led if we see a pulse, so that test equipment would be suficient to test if the clear signal is stuck in reset. BTW a hand held logic probe is not the proper tool to use to verify operation of a 7474, I merely presented that to show how to test that one failure mode, there are many more, and you will need to see more than one signal to check.
     
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