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P5040/P5020 Reference Design Board User Guide, Rev. 0
66
Freescale Semiconductor
Programming Model
The PX_WATCH register has the following characteristics:
•
Represents the eight most significant bits of an internal 34-bit watchdog timer.
•
New values MUST be written before the PX_VCTL[WDEN] bit is set to ‘1’.
•
Rewrites new values (except the PX_VCTL[GO] bit) every time the register is reset due to timeout
or other reset/restart conditions.
•
Time formulae:
— Timer Base = 26-bits x 30ns interval = 2.01326592 seconds
— where the upper 8-bit field represents (seconds)
[(decimal value of the 8-bit field) x (2.01326592sec)] + 2.01326592sec
This table lists examples of PX_WATCH register values.
7.1.24
Switch Register (PX_SWx)
The switch register defines configuration switch overrides. Each SWx register and its bits correspond to a
similarly named board switch.
If a matching ENx bit is set then the value written to the corresponding register bit is selected, not the
corresponding DIP-switch.
Table 51. PX_WATCH Field Descriptions
Bits
Name
Description
0–7
WVAL
• R - Returns current programmed values.
• W - Sets the watchdog timer.
Table 52. Watchdog Timer Values
Timeout Value
Timeout
Binary
Hex
11111111
0xFF
0.59 min
01111111
0x7F
4.29 min
00111111
0x3F
2.15min
00011111
0x1F
1.07 min
00001111
0x0F
32.1 sec
00000111
0x07
16.1 sec
00000011
0x03
8.05 sec
00000001
0x01
4.027 sec
00000000
0x00
2.013 sec