Cirrus Logic EP93xx - Manual (Page 768)

26-6 DS785UM1
Copyright 2007 Cirrus Logic
Keypad Interface
EP93xx User’s Guide
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26.2.4 Low Power Mode
The key scanning block also supports a low power wake-up mode. In this mode, a key press
generates a wake up interrupt. The key scan interrupt should be masked. Because the wake
up interrupt is asynchronous, and depends on external keypad lines which may have a large
capacitance value, glitches may occur on the interrupt when transitioning to low power mode.
After transitioning, all clocks to the key scanning circuitry can be shut down. In the low power
mode, all of the column line drivers should be in input mode in a high state due to the pad pull
up resistors. The column inputs are ANDed together to detect any key presses. This signal
directly toggles the interrupt output. The detect condition is not de-bounced.
26.2.5 Three-key Reset
The key scanning circuitry provides a three-key reset output by detecting keys (columns) 2,
4, and 7 activated in row 0. The three-key reset detect is used by the watchdog circuit to
generate a three-key initiated reset to the system.
The output RESET_KEYS_DETECTED goes to the Watchdog block to indicate that a three-
key reset is being requested.
26.3 Registers
Note: Key scan controller registers are intended to be word accessed only. Since the least
significant bytes of the address bus are not decoded, byte and half word accesses are not
allowed and may have unpredictable results.
Register Descriptions
KeyScanInit
Table 26-1. Keypad Interface Register Memory Map
Address Name SW locked Type Size Description
0x808F_0000 KeyScanInit No Read/Write 24 bits Key Scan Initialization Register
0x808F_0004 KeyDiagnostic No Read/Write 6 bits Key Scan Diagnostic Register
0x808F_0008 KeyRegister No Read Only 16 bits Key Value Capture Register
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
RSVD DBNC
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
DIS3KY DIAG BACK T2 NA PRSCL