1 / 12

Designing State Machines for Numeric Keypads in Computer Engineering Labs

This guide discusses the design of state machines for detecting key presses on numeric keypads, specifically within the context of an EE 316 Computer Engineering lab setting. Key topics include choosing between Mealy and Moore state machines, addressing clock frequency concerns, and managing debouncing issues. The document outlines the hardware requirements for implementing a keypad state machine on a GAL22V10 chip, as well as necessary output specifications for scanning columns. Theoretical insights from John Wakerly's "Digital Design Principles and Practices" are also integrated for a deeper understanding.

melanie-burks
Télécharger la présentation

Designing State Machines for Numeric Keypads in Computer Engineering Labs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Designing State machines for a numeric Keypad EE 316 Computer Engineering Junior Lab

  2. Topics • Designing a state machine to detect key press • PLD based design • Mealy or Moore? • Is clock frequency an issue? • Debouncing issues

  3. Keypad Hardware State Machine Column Scan 9 Outputs? 1 1 } Code for Key press: Output of the State machine 1 GAL22V10 1 Detection of Key press=> input to the state machine Ready or Enable Clock http://www.webopedia.com/TERM/n/numeric_keypad.html

  4. Design alternatives • Which of the two state machines, Mealy or Moore, should we use? • Since we need 9 outputs for the state machine, 9 flip-flops are used up. Can we fit the keypad state machine on a single GAL chip?

  5. GAL22V10 • Max 22 inputs • Max 10 outputs • 8-16 Product terms 8 Product terms for this macrocell Ref: Digital Design Principles & practices, John Wakerly

  6. State-machine structure (Mealy) Output can change asynchronously with the change of input. • Do we need to add debouncing circuits? • Or, should we use a pipelined version of Mealy? Ref: Digital Design Principles & practices, John Wakerly

  7. State-machine structure (Moore) • Do we need keypad debouncing circuits? • How many flip-flops do we need? Ref: Digital Design Principles & practices, John Wakerly

  8. Fitting the State Machine on a GAL chip 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 5 V 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 4.7 K Key press detect

  9. A Moore State machine Input State Output key code, Ready Scan 1111 One input is 0 One input is 0 Resolved 4 code/1 Key press Detect Key detect 4 1111/0 Key detect 1 1111/0 Key detect 1 1111/0 State 1 1111/0 Valid Output One input is 0 1111 1111 Resolved 1 code/1 12 States? 4 or more Flipflops? 0111 - 7 1011 - 11 1101 - 13 1110 - 14 0011 - 3 0001 - 1 1001 - 9 1000 - 8 1100 - 12 0100 - 4 0110 - 6 0010 - 2 State 4 1111/0 State 2 1111/0 1111 1111 Resolved 3 code/1 One input is 0 1111 1111 State 3 1111/0 Key detect 2 1111/0 Key detect 2 1111/0 Key detect 3 1111/0 Resolved 2 code/1 One input is 0 1111

  10. Fitting the State Machine on a GAL chip 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 State 1? State 2? State 3? 5 V State 4? 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 4.7 K Key press detect We use part of the state variables as outputs of the state machine to be used for column scan.

  11. A Mealy State machine Input/key code, Ready One input is 0/code, 1 One input is 0/code, 1 1111/1111, 0 One input is 0/1111, 0 Key detect State 4 Key detect State 1 State 1 1111/0 One input is 0/1111, 0 1111/1111, 0 1111/1111, 0 00111 - 7 01011 - 11 01101 - 13 01110 - 14 10111 – 3 11011 – 9 11101 - 12 11110 - 6 1111/1111, 0 State 4 1111/0 State 2 1111/0 One input is 0/1111, 0 1111/1111, 0 1111/1111, 0 1111/1111, 0 State 3 1111/0 Key detect State 2 Key detect State 3 One input is 0/code, 1 One input is 0/code, 1 One input is 0/1111, 0 1111/1111, 0

  12. How to choose the proper clock frequency • The clock frequency should be slow enough so that period is comparable to or larger than the keypad bouncing times. • The clock frequency should be fast enough so that it will be able to detect the key press even if it is released very quickly

More Related