Presentation is loading. Please wait.

Presentation is loading. Please wait.

EKT 221 : Digital 2 MUX-based Transfer. Multiplexer-Based Transfers A dedicated multiplexer is used to select the wanted input. A simple technique using.

Similar presentations


Presentation on theme: "EKT 221 : Digital 2 MUX-based Transfer. Multiplexer-Based Transfers A dedicated multiplexer is used to select the wanted input. A simple technique using."— Presentation transcript:

1 EKT 221 : Digital 2 MUX-based Transfer

2 Multiplexer-Based Transfers A dedicated multiplexer is used to select the wanted input. A simple technique using multiplexers for selection is introduced to allow multiple microoperations on a single register. From previous lecture, we saw that multiplexers and parallel load registers can be used to implement dedicated transfers from multiple sources.

3 Dedicated MUX – based Transfer Three n-bit 2:1 MUX, each with its own SELECT signal ◦ MUX0 : S0 ◦ MUX1 : S1 ◦ MUX2 : S2 Each register has its own LOAD signal ◦ R0 : L0 ◦ R1 : L1 ◦ R2 : L2 MUX0 MUX1 MUX2 S0 S1 S2 SELECT L0L1 L2 LOAD

4 Dedicated MUX – based Transfer Multiplexer connected to each register input produces a very flexible structure Characterize the simultaneous transfers possible with this structure

5 S0, S1, S2 = (0,0,1) and L0, L1, L2 = (0,0,1) then L2 : R2 ← R1 Example 1:

6 S0, S1, S2 = (1,0,0) and L0, L1, L2 = (0,1,1) then L1: R1 ← R0, L2 : R2 ← R0 Example 2: L1: R1 ← R0, L2 : R2 ← R0

7 MUX and Bus – based transfer for Multiple Registers A typical digital system has many registers. Paths must be provided to transfer data from one register to another. Multiplexer dedicated to each register has problems: ◦ Excessive amount of logic ◦ High number of interconnections

8 MUX and Bus – based transfer for Multiple Registers Solution to the problem : Use a shared transfer paths for registers ◦ A shared transfer object is called a bus ◦ A bus is characterized by a set of common lines, with each line driven by selection logic. Bus implementation using : ◦ Multiplexers ◦ Three – state nodes and drivers In most cases, the number of bits is the length of the receiving register

9 Multiplexer Bus Only need a single n-bit 3:1 MUX and parallel load registers. MUX outputs are shared as a common path (bus)

10 Multiplexer Bus SELECT signal ◦ Determines the contents of single source register that will appear on the MUX outputs. ◦ 000 : R0 ◦ 011 : R1 ◦ 102 : R2 LOAD signal ◦ Determine the destination register / registers to be loaded with the bus data 0 1 2

11 Multiplexer Bus S1, S0 = (0,0) and L0, L1, L2 = (0,0,1) then L2 : R2 R0 Example 1:

12 Multiplexer Bus Example 2: S1, S0 = (1,0) and L0, L1, L2 = (1,1,0) then L0: R0 R2, L1 : R1 R2

13 Example 3: S1, S0 = (1,0) and L0, L1, L2 = (0,1,1) then L1: R1 R2, L2 : R2 R2 (no change) Multiplexer Bus

14 A single bus driven by a MUX lowers cost, but limits the available transfers Characterize the simultaneous transfers possible with this structure… Characterize the cost savings compared to dedicated MUX…

15 Multiplexer Bus 3 rd transfer : cannot be done ◦ Requires 2 simultaneous sources (R0 and R1) on a single bus ◦ Cannot occur in 1 clock cycle ◦ This transfer requires at least 2 buses ◦ However, dedicated MUX can do this transfer

16 MUX-based vs Bus-based MUX-based ◦ Any combination of transfers is possible Bus-based ◦ Simultaneous transfers from different sources in single clock cycle is impossible ◦ Reduction in hardware ◦ Limitation in simultaneous transfers

17 Three – State Bus The 3 – input MUX can be replaced by a 3 – state node (bus) and 3 – state buffers Cost is further reduced Signals can travel in 2 directions Use same bus to carry signals into and out of registers

18 Three – State Bus LOAD signal ◦ L0 : R0 ◦ L1 : R1 ◦ L2 : R2 ENABLE signal ◦ E0 : R0 ◦ E1 : R1 ◦ E2 : R2

19 Three – State Bus A register with n lines that serve as both inputs and outputs. 3-state buffers are enabled: ◦ The n lines are OUTPUTS. 3-state buffers are disabled: ◦ The n lines are INPUTS.

20 Three – State Bus Multiplexer Bus

21 Thank You


Download ppt "EKT 221 : Digital 2 MUX-based Transfer. Multiplexer-Based Transfers A dedicated multiplexer is used to select the wanted input. A simple technique using."

Similar presentations


Ads by Google