notes-326-set10

notes-326-set10 - Registers & Counters Objectives This...

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1 1 Elec 326 Registers & Counters Registers & Counters ± Objectives This section deals with some simple and useful sequential circuits. Its objectives are to: ² Introduce registers as multi-bit storage devices. ² Introduce counters by adding logic to registers implementing the functional capability to increment and/or decrement their contents. ² Define shift registers and show how they can be used to implement counters that use the one-hot code. ± Reading Assignment ² Sections 4.4 and 5.4 2 Elec 326 Registers & Counters 1. Registers ± A register is a memory device that can be used to store more than one bit of information. ± A register is usually realized as several flip-flops with common control signals that control the movement of data to and from the register. ² Common refers to the property that the control signals apply to all flip-flops in the same way ² A register is a generalization of a flip-flop. Where a flip- flop stores one bit, a register stores several bits ² The main operations on a register are the same as for any storage devices, namely ³ Load or Store: Put new data into the register ³ Read: Retrieve the data stored in the register (usually without changing the stored data
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2 3 Elec 326 Registers & Counters ± Control Signals ² When they are asserted, they initiate an action in the register ² Asynchronous Control Signals cause the action to take place immediately ² Synchronous Control Signals must be asserted during a clock assertion to have an effect ± Examples ² On the following three registers, which control signals are asynchronous and which are synchronous? How are the control signals asserted? 4 Elec 326 Registers & Counters DQ Q CLR STO D 0 D 1 D n-1 Q n-1 Q 0 Q 1 Q CLR Q CLR CLR module reg1 (STO, CLR, D, Q); parameter n = 16; input STO, CLR; input [n-1:0] D; output [n-1:0] Q; reg [n-1:0] Q; always @( posedge STO or negedge CLR) if (CLR ==0) Q <= 0; else Q <= D; endmodule
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3 5 Elec 326 Registers & Counters JQ Q K Q K Q K D 0 D 1 D n-1 Q n-1 Q 0 Q 1 LD CLK CLR OE 6 Elec 326 Registers & Counters DQ Q Q Q D 0 D 1 D n-1 Q n-1 Q 0 Q 1 LD CLK CLR OE
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notes-326-set10 - Registers &amp; Counters Objectives This...

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