User Manual

11-2 EP7309/11/12 User’s Manual - DS508UM4

General Purpose I/O (GPIO)

Programming Example

;*******************************************************************

; Enable GPIO Port B as Outputs. Set pins 0-3 high 4-7 low

;*******************************************************************

DATADIR EQU 0xFF

PORTB EQU 0x0F

;

ldrb r1, =DATADIR

strb r1, [r12, #0x41] ; Set direction as output

ldrb r1, =PORTB

strb r1, [r12, #0x1] ; Set PORTB initial condition

;

Operational Overview

PADDR, PBDDR, an d PEDDR determine the direction of each of the GPIOs in their

respective port. If set, th e corresponding GPIO will be configured as an output. I f

cleared, th e GPIO is treated as an input.

PDDDR determines the direction of PORTD. Initial state is low (output). High sets

pins as inputs.

Values read from these register, when configured as i nputs, reflect th e external state of

the pin. Values written to these pins, i.e. logic 1, when configured as an output, will

cause the logic st ate change from 0 to 3.3 V DC. All bits are cleared by a system reset.

Multiplexed Pins

Port A can be used to detect a keyboard entry to generate on e of several internal

conditions as mentioned in the keyboard interface discussion.

PD6 and PD7 are multiplexed with SDRAM byte m asks SDQM0 and SDQM1

respectively.TobeusedasGPIOs,SYSCON3bit10mustbeset.

Port E, at power-on-reset, pins [1:0] are read during power-on-reset d etermi ne the

memory width of the boot ROM to the CP U . See the boot ROM discussion for m ore

details. After boot up, these pins are treated as GPIOs only.

See “General Purpose I/O (GPIO) R egister Li st” on p age 11-1 and Operational

Overview.