Hardware Reference
In-Depth Information
Consequently, when budgeting your 3.3 V supply current, factor in the following:
GPIO:
Current used for each GPIO
output
pin assigned (2 mA
to 16 mA)
+3.3 V:
All current going to circuits powered from P1-01, P1-17,
and P5-02.
MAX232CSE:
If you attached a RS-232 adapter, allow for about
15 mA.
To save on your power budget, configure unused GPIO pins as inputs.
Configuration
Each GPIO pin is affected by several configuration choices:
•
General-purpose input, output, or alternate function
•
Input event detection method
•
Input pull-up/pull-down resistors
•
Output drive level
Alternate Function Select
When a GPIO pin is configured, you must choose whether it is an input, an output, or an
alternate function (like the UART). The complete list of choices is shown in Table
10-4
.
The exact nature of what
alternate function x
means depends on the pin being configured.
Table 10-4.
Alternate Function Selection
Code
Function Selected
ALT
000
GPIO pin is an input.
001
GPIO pin is an output.
100
GPIO pin is alternate function 0.
0
101
GPIO pin is alternate function 1.
1
110
GPIO pin is alternate function 2.
2
111
GPIO pin is alternate function 3.
3
011
GPIO pin is alternate function 4.
4
010
GPIO pin is alternate function 5.
5
