EKT 221 : Digital 2 Serial Transfers & Microoperations

1. EKT 221 : Digital 2Serial Transfers & Microoperations

2. Serial Transfers & Microoperations • Serial transfers • Used for “narrow” transfer paths • Example : Telephone or cable line • Parallel – to – Serial : at source • Serial – to – Parallel : at destination • Serial micro-operations • Example 1 : Addition • Example 2 : Error – Correction for CDs Serial  Parallel Parallel  Serial Source Destination

3. Serial Transfers & Microoperations • Serial mode in digital system: information in the system is transferred or manipulated one bit a time. • Information is transferred one bit at a time by shifting the bits out of one register and into a second register. • This transfer method is in contrast to parallel transfer, in which all the bits of the register are transferred simultaneously at the same time (during one clock pulse).

4. Serial Transfers • Serial mode  info is transferred / manipulated one bit at a time • Serial transfer of information from Reg A to Reg B is done with shift registers

5. Serial Transfers • Serial output (SO) of Reg A connected with serial input (SI) of Reg B • SI of Reg A receives 0’s while data from Reg A are transferred to Reg B • Initial content of Reg B shifted out to its SO and lost

6. Serial Transfers • To maintain the data in Reg A, • connect SO of Reg A to its SI • Information is circulated back into Reg A

7. Serial Transfers • Shift determines when & how many times the registers are shifted • Clock pulse (Clock) can pass to shift register clock inputs C only when Shiftis HIGH (1)

8. Serial Transfers • Each shift register has four stages. • Shiftsignal must be designed for a fixed time of four clock pulses. • Shift in HIGH : Clock inputs C  T1, T2, T3 and T4 • Shift in LOW : Clock inputs C  HIGH Shift Reg disabled, shifts stop Shift Reg enabled, Shift occurs in both registers

9. Serial Transfers SI (A) = 0 Reg B = Previous value of Reg A

10. Serial Micro-operations • Serial addition is a low cost way to add large numbers of operands, since a “tree” of full adder cells can be made to any depth. • Other operations can be performed serially as well, such as parity generation / checking or more complex error – check codes. • Shifting a binary number left = multiplying by 2 • E.g sl 0100  1000 • Shifting a binary number right = dividing by 2 • E.g sr 0100  0010

11. Serial Adder – demonstrate the serial mode operation • The circuit shown uses 2 shift registers for operands • A (3:0) and B (3:0) • A full adder (FA), and one more FF (for carry) is used to compute the sum • Result (sum) stored in Reg A and final carry stored in FF

12. Serial Adder – demonstrate the serial mode operation SHIFT = 1 Result (sum) stored in Reg A Final carry stored in FF Both registers are shifted once to right Carry FF = 0

13. Serial Adder • SI of Reg B can receive new inputs • In each clock pulse/cycle : • New sum bit is transferred to Reg A • New carry transferred to FF • Both registers shifted once to the right • Process continues until Shift = 0

14. Analyzing the circuit : Serial Adder Example 1: Find value in Reg A after 4 shifts. Reg A : 1000 Reg B : 0101

15. Analyzing the circuit : Serial Adder ANSWER : 1101, after 4 clock cycle

16. Analyzing the circuit : Serial Adder Example 1: Find value in Reg A after 4 shifts. Reg A : 1011 Reg B : 0101

17. Analyzing the circuit : Serial Adder 1 is indicated in Cout ANSWER : 10000, after 4 clock cycle

18. Sin Sin A0 FA S0 B0 B0 A0 Reg B Reg A Cin A1 B1 A2 B2 S1 FA B3 A3 A1 B1 Sout Sout FA S2 A2 B2 FA S3 A3 B3 Cout Parallel Adder Can be the input for Reg A

19. Serial Vs Parallel Transfers • Space Vs Time Trade-off • Serial adder is a sequential circuit because it includes the carry from FF. But need n clock cycle to complete the addition (Less Space, more Time) • Parallel adder is a combinational circuit because it needs n FA for n bit operation. Need only one clock cycle to complete the addition. (More Space, less Time) • Gives the designer choice. • More Space – More cost • More Time – More delay (not fast)

20. Thank You