Cirrus Logic EP93xx - Manual (Page 763)

DS785UM1 26-1
Copyright 2007 Cirrus Logic
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Chapter 26
26 Keypad Interface
26.1 Introduction
Note: This chapter applies only to the EP9307, EP9312, and EP9315 processors.
The keypad interface has the following features:
• A maximum 8x8 array of normally open, single pole contacts
• A back drive feature to minimize capacitance effects
• A typical scan count limit of 3 consecutive scans
• A maximum mechanical bounce time for a key press of 20 milliseconds
• A typical interrupt interval between 24 and 44 milliseconds
• A low-power wakeup mode
• A three-key reset
If the system does not use a keyboard, the Row[7:0] and Column[7:0] pins can be remapped
to General Purpose Input/Output (GPIO) pins. For details, see
Chapter 5 , “DeviceCfg” on
page 5-25 and Chapter 28 , Table 28-4 on page 28-8 .
A block diagram for the key array scanning circuitry is shown in Figure 26-1 .
Figure 26-1. Key Array Block Diagram
Precounter
Debounce Counter
Row/Collumn
Counter
Pipeline
Scan
Control
Row Decoder
Column Mux
Temp Key Regs Key Regs
Interrupt
Controller
3 Key Reset Key Detector
Diagnostics
Equal
Compare
Pipeline
Row lines
Column lines
Inactive
Interrrupt
3 Key Reset