The 74195 may also be used to load a 4-bit value in parallel (all bits at once,
ID: 2072591 • Letter: T
Question
The 74195 may also be used to load a 4-bit value in parallel (all bits at once, ie, Parallel-ln), then output each bit serially ie, one bit at a time (Serial-Out), beginning with the LSB first. The acronym for this is PISO. Set the SHIFT/LOAD input to activate the Load function. Note that this enables the parallel data inputs (A thru D). Set the parallel inputs (A to D) to 1100_2. "Parallel load" the shift register with this number by CLOCK'ing the shift register once. What 4-bit Binary value displays on the QA thru QD outputs? ___________ Note that unlike the serial-in operation, the LSB (0) of the number is instantly available on QD. 3. Set the SHIFT/LOAD input to activate the Shift function and set the Serial DATA Input LOW. Record the initial bit value of QD (LSB) below: CLOCK the shift register 3 more times and record the bit value of QD after each successive clock pulse in the remaining 3 locations below: 1^st QD (LSB):_____: Subsequent QD bit values: ___ ___ ____. Remembering that bits are shifted out in reverse order, Reverse the order of the 4 bits you recorded and write that 4-bit binary number here: ______ ? Is this the same value originally loaded into the shift register? _________ Repeat steps 1 and 2 using several of your own numbers to convince yourself of the shift operation.Explanation / Answer
2) Parallel loading means that all bits are available on the outputs at once.
Thus, the 4-bit binary value that's displayed is: 1100
4) Initial bit value of QD is the LSB of the input number, that is 0.
5) Bits are shifted out in reverse order, beginning from the LSB. Thus, the order of QD values is: 0 => 0 => 1 => 1
Reversing the order of bits gives the following 4-bit number: 0011
No, this is not the same as the original number.
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