1. Digital Electronics

2. Registers and Counters
Chapter 6
Registers and Counters

3. Some Terminology
A Register is a group of flip-flops. Each FF is capable of storing one bit of information
A Shift Register is a register capable of shifting its binary information in or both directions
A Counter is a register that goes through a prescribed sequence of states upon the application of input pulses

4. A 4-bit Shift Register

5. Copy Register A to B

6. Universal Shift Register

7. Universal Shift Register
Function Table
Mode Control
S S Register Operation
No Change
Shift Right
Shift Left
Parallel Load

8. Binary Ripple Counter
Counts in binary from 0000 through 1111 (16 states)
The clock for the second T- FF comes from the output of the first T-FF etc. There is no common clock
The count ripples through like a “bucket-brigade”. This can slow things down as the number of FF’s increases.

9. Ripple Counter with D-FF

10. BCD Ripple Counter
Counts in BCD from 0000 through 1001 (10 states) a.k.a. “mod 10” or “decimal” counter
The clock for the second T- FF comes from the output of the first T-FF etc. There is no common clock
When the count is 1001 then Q8 =1 so Q2 stays at 0 which means Q4 stays at zero. Hence the next count is 0000

11. 4-bit Synchronous Binary Counter
Pin E is count enable feature.
The clock is common for all 4 JK FF’s
The “next stage” output is used to cascade another 4-bit counter to make an 8-bit counter E

12. Binary Counter with Load

13. Two BCD Counter Ideas
Loads 0000 after Clears on seeing 1010

14. VHDL for Binary Counter
module counter (Count,Load,IN,CLK,Clr,A,CO);
input Count,Load,CLK,Clr;
input [3:0] IN; //Data input
output CO; //Output carry
output [3:0] A; //Data output
reg [3:0] A;
assign CO = Count & ~Load & (A == 4'b1111);
(posedge CLK or negedge Clr)
if (~Clr) A = 4'b0000;
else if (Load) A = IN;
else if (Count) A = A + 1'b1;
else A = A; // no change, default condition
endmodule

15. That’s All Folks!