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Intel® PXA255 Processor Developer’s Manual 4-19
System Integration Unit
4.1.3.7 Example Procedure for Configuring the Alternate Function Registers
In this example, GP0 is used as a generic GPIO and GP[15:1] are configured as their alternate
functions. Refer to Table 4-1 for the list of alternate functions. No other GPIOs are configured.
After the de-assertion of any RESET, GPDR0[15:0] configures GPIO pins in this example to be
inputs. GAFR00[31:0] will be 0x0000_ 0000 to indicate normal GPIO function. For simplicity,
assume that GP[16-31] are inputs configured as normal GPIOs.
In this example,
• GPIO[0] is configured as a normal GPIO input
Table 4-28. GAFR2_L Bit Definitions
Physical Address
0x40E0_0064
GAFR2_L System Integration Unit
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
AF79 AF78 AF77 AF76 AF75 AF74 AF73 AF72 AF71 AF70 AF69 AF68 AF67 AF66 AF65 AF64
Reset
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
<31:0> AF[x]
GPIO Pin ‘x’ Alternate Function Select Bits (where x=64 through 79).
A bit-pair in this register determines the corresponding GPIO pin’s functionality as one of
the alternate functions that is mapped to it or as a generic GPIO pin.
00 – The corresponding GPIO pin (GPIO[x]) is used as a general purpose I/O.
01 – The corresponding GPIO pin (GPIO[x]) is used for its alternate function 1.
10 – The corresponding GPIO pin (GPIO[x]) is used for its alternate function 2.
11 – The corresponding GPIO pin (GPIO[x]) is used for its alternate function 3.
Table 4-29. GAFR2_U Bit Definitions
Physical Address
0x40E0_0068
GAFR2_U System Integration Unit
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved AF84 AF83 AF82 AF81 AF80
Reset
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
<31:10> — reserved
<9:0> AF[x]
GPIO Pin ‘x’ Alternate Function Select Bits (where x=80 through 84).
A bit-pair in this register determines the corresponding GPIO pin’s functionality as one of
the alternate functions that is mapped to it or as a generic GPIO pin.
00 – The corresponding GPIO pin (GPIO[x]) is used as a general purpose I/O.
01 – The corresponding GPIO pin (GPIO[x]) is used for its alternate function 1.
10 – The corresponding GPIO pin (GPIO[x]) is used for its alternate function 2.
11 – The corresponding GPIO pin (GPIO[x]) is used for its alternate function 3.