Power consumption report ST72F324 MCU board

1
Key scanning
February, 2004
MCU / Shanghai
2
Agenda

• Key-scan basics
• implementation
• Key-scan library

3
Direct port-line or column-row scanning

• Direct port-line suitable for several keys(lt10),
  1 port line / key
• column-row scanning suitable for 10100 keys, M
  column N row supports up to MN keys

4
Key-scan tasks

• Key press/ release probing
• Ghost-key condition detection
• Key debouncing
• Taking appropriate action Output the status

5
Key-scan illustration

• Column,row same stable logical level(high level
  here)
• Output to column sequentially

6
Ghost key

• 3 corners of a rectangle are pressed down
• Hardware solution to use diodes to avoid the
  ghost condition
• Software solution to detect ghost-key condition
  and give warning

7
Key debouncing

• Key bounce is the general characteristic of
  mechanical key/switch
• solution hardware and software debouncing

8
Agenda

• Key-scan basics
• implementation
• Key-scan library

9
Key-scan block diagram
MCU
Taking Proper actions
Column Port line
Row Port line
Keyboard matrix
10
Software flow chart
Reset entry
Wait for Scan time
Perform key-scan Detecting ghost-key
Key debouncing
Key pressed /released detected?
N
Y
Take actions
11
Scan-key flow chart
Entry
Output low to Column, delay
Read from row Compare and store Output high to
column Column
N
Y
Last column?
Ghost key?
Return ghost key
Return key pressed/released, Or no change
12
Key debouncing state machine-press
13
Key debouncing state machine- release
14
Agenda

• Key-scan basics
• implementation
• Key-scan library

15
Key-scan library

• Target to ease users work and time
• Support 188 key-matrix, easy to port to other
  matrix (only several minutes needed) under
  HIWARE C compiler
• Embedded key-scan function, ghost-key detection,
  debounce function
• Verified in Bluetooth keyboard

16
Key-scan library interface
Init_KB_Lib
Initialization code
call
Main routine
Exe_KeyScan
Confirm_KeyScan
Output_Column
Wait_10us
Call back
Input_Row
Library
User Program
17
Key-scan library prototype

• void Init_KB_Lib(void)
• struct Key_Result
• unsigned char Code // row-column value
• // special value code0xfe ghost key code0xff
  no key-state changed
• unsigned char State // 0 default 1 pressed
  2 released
• struct Key_Result Exe_KeyScan(void)
• void Confirm_KeyScan(unsigned char code)
• // confirm key-scan event(pressed or released)
• // means proper action succeeded or failed
  code0 succeeded, code1 failed