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Port B GPIO Functionality

5.3.3 Looping Data on Port B

Example 5-3 shows how to configure Port B pins to allow looping data from an output back to an input.

Example 5-3. Loop-Back Example

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

 

 

;* LOOPBACK example*

 

 

;* for Port B

*

 

 

;* of DSP56824 chip *

 

 

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

 

 

START

EQU

$0040

; Start of program

BCR

EQU

$FFF9

; Bus Control Register

PBD

EQU

$FFEC

; Port B Data

PBDDR

EQU

$FFEB

; Port B Data Direction Register

PBINT

EQU

$FFEA

; Port B Interrupt Register

data_o

EQU

$0001

; data output

data_i

EQU

$0001

; data input

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

 

 

 

;* Vector setup*

 

 

 

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

 

 

 

ORG

P:$0000

 

; Cold Boot

JMP

START

 

; also Hardware RESET vector (Mode 0, 1, 3)

ORG

P:$E000

 

; Warm Boot

JMP

START

 

; Hardware RESET vector (Mode 2)

ORG

P:START

 

; Start of program

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

 

 

 

;* General setup*

 

 

 

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

 

 

 

MOVEP

#$0000,X:BCR

; External Program memory has 0 wait states.

 

 

 

; External data memory has 0 wait states.

 

 

 

; Port A pins are tri-stated when no

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

 

 

; external access occurs.

 

 

 

;* Port B setup*

 

 

 

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

 

 

 

MOVEP

#$0000,X:PBINT

; Disable GPIO interrupt requests on

 

 

 

; all lower eight Port B pins (default).

MOVEP

#$FF00,X:PBDDR

; Select pins PB0-PB7 as input and

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

 

 

; pins PB8-PB15 as output.

 

 

 

;* Main routine*

 

 

 

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

 

 

; ...

 

 

 

LOOPBACK

 

 

; Test Loop

MOVE

X:data_o,X0

; Put bits 8-15 of “data_o” on pins PB8-PB15.

MOVEP

X0,X:PBD

; Bits going to input pins are ignored.

 

 

 

; ...

MOVEP

X:PBD,X0

; Read PB0-PB7 into bits 0-7 of “data_i”.

MOVE

X0,X:data_i

; Bits 8-15 get values of PB8-PB15 as well.

BRA

LOOPBACK

; ...

 

 

 

 

 

5-10

DSP56824 User’s Manual

 

Соседние файлы в папке DSP568xx