9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU1 Other FF Types

9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU2 Class 24-Other FF Types  Using the preset and clears  Other FF types The D The SR The JK The T (Toggle)  Don’t cares  Material from section 5-5 and 5-6 of text

Use of the presets and clears  Remember our circuit from before  The specification: The circuit will have one input, X, and one output, Z. The output Z will be 0 except when the input sequence 1101 are the last 4 inputs received on X. In that case it will be a 1.  Now add the part that it starts up and assumes that a 1 was the previous input. Therefore it starts, after a reset, in state B. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU3

State B of the system  State B has a coding of 01 so we want the initial state of the FFs to be 01.  Have the circuit shown here. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU4

Setting up a RESET’ input  Now have a RESET’ input with is active low. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU5

Other FF Types – The D  Have already looked at and used the D FF Information on it for a equal comparison to the other types. Characterstic Table Char. Equation Excitation Table 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU6

Other FF Types – The SR  Have already looked at and used the SR FF Information on it for a equal comparison to the other types. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU7

Other FF Types – The JK  The JK have some logic before the FF. This can reduce the discrete logic needed to generate the next state. Could be very helpful when using individual gate chip technology. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU8

Other FF Types – The T FF  The T FF or the Toggle FF. Same as with the JK type FF, the Toggle could reduce the discrete logic needed for implementation. Very useful in counting circuits. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU9

A counter with T FFs  A 3-bit up counter.  Will count 000  001  010  011  100 etc. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU10

What about unused states?  A circuit with n flip-flops can have up to 2 n binary states.  Consider the problem in the text.  The specification is given in the truth table. The system has 3 flip-flops and one input X. There is no output column which means the current value of the FFs is the output of the circuit.  With 3 flip-flops a total of 8 state are possible but only 5 are specified. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU11

The state table  States 0000, 0001, 1100, 1101 and 1110, 1111 are not listed. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU12

Generation of the next state  The K-maps for next state generation. 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU13

Class 24 assignment  Covered sections 5-6  Problems for hand in Nothing new  Problems for practice Nothing new  Reading for next class: 7-1 9/15/09 - L24 Other FF TypesCopyright Joanne DeGroat, ECE, OSU14