MicroP-Lab4(Subroutines & Parallel Port)

7/23/2019 MicroP-Lab4(Subroutines & Parallel Port)

1/12

SUBROUTINES AND PARALLEL PORT


2/12

Objectives of the Lab Learn how to make subroutines

Function of call and return statement

Writing Data on Parallel Port Pins

Writing a Delay Procedure


3/12

Making Subroutines in P The keywords proc and endp used in subroutine are like

brackets in C++. The syntax to write a subroutine is:

procedure_nameproc

Coding done here

.

.

ret

procedure_name endp


4/12

Using Subroutines in P

.startup

coding statements

call subroutine1

call subroutine2

.exit

subroutine1proc

coding statements

ret

subroutine1 endp

subroutine2proc

coding statements

ret

subroutine2 endp

end

To use a subroutine, we just use the call statement with the

procedure_name. Below is the structure to write a code using

subroutines.


5/12

Use of CALL and RET The call and ret statements have a control over how the

instruction pointer works. The sequence is given below:

1. When the call statement is invoked, the address to the next

instruction (in main routine) is saved on the stack.

2. IP gets the offset address of the first instruction of the procedure

which transfers the control to procedure.

3. When ret statement is found in the subroutine, the control is

transferred back to the main routine.


6/12

Parallel Port Pins

Status Register

Data Register

Control Register

Pins 18-25: Ground


7/12

Writing data to parallel port pins First of all, to write the data on any register (data register), one

must have the address of the register.

And then a command that is able to write the data on the

specific register.

The address of data register is 378h, and the command to write

data is out reg,data.

The data can be put by a simple 3 line instruction sequence,

mov ax,data => mov dx,378h => out dx,ax


8/12

Instructions used in this Lab1. CALL (Call a subroutine)

2. RET (out of the subroutine)

3. OUT (write data to a register)

4. ROL reg, no. of rotates (rotate bits left)

5. ROR reg, no. of rotates (rotate bits right)


9/12

Writing a delay procedure.startup

code calling delay

.exit

delayproc

mov dx,15000

l1:dec dx

mov bx,0ffffh

l2:

dec bx

cmp bx,0

jne l2

cmp dx,0

jne l1

retdelay endp

end


10/12

Code for led pattern moving right.startup

mov al, feh

mov ah,al

start:

mov dx, 378h

out dx,ax

ror ax,1

calldelay

jmp start

.exit

delay proc

delay endp

end

LEDs will beattached toPP to generate

patterns.


11/12

Code for led blinking.startup

Start:

mov ax, 0ffffh

mov dx, 378h

out dx,ax

calldelay

mov ax, 0h

mov dx, 378h

out dx,ax

jmp start

.exit

delay proc

delay endp

end

?


12/12

Lab Tasks1. Move LED pattern towards right on parallel port.

2. Blink LEDs on parallel port. (Quiz next time, expect

subroutines also with all previous commands)

MicroP-Lab4(Subroutines & Parallel Port)

Documents

Transcript of MicroP-Lab4(Subroutines & Parallel Port)