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Terminating a loop

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JimL

Post subject: Terminating a loop

Posted: Thu Dec 22, 2016 5:39 pm

Joined: Thu Dec 22, 2016 5:21 pm
Posts: 2

Hi, I'm after some help and yes this is with an assignment but a rather specific part with which I've become a little bogged down and no amount of research seems to have helped clarify this for me. I'm making a timer that starts and stops when the user presses a key to start and stop the program. I've used the below to read the single character which starts the program fine. I get this is because the following sits outside of my timer loop and so just waits for a user input before calling the time and entering the loop

Code:

    MOVE    #5,D0
            TRAP    #15

I want the timer to be printed continuously until the user presses a key again and the program will then end. My issue is reading the second key press as using task #5 the program sits there until a key is pressed and thus the loop stops. Is there a way around this? Perhaps where a finite amount of time is spent waiting for the second input? I think I/O Task#7 may be of use but I cant find out much about it's use.

Any help would be greatly appreciated.

Jim.

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profkelly

Post subject: Re: Terminating a loop

Posted: Thu Dec 22, 2016 7:21 pm

Joined: Thu Dec 16, 2004 6:42 pm
Posts: 1101

I through something together. Trap task 7 is used to test for keyboard input.

Code:

*-----------------------------------------------------------
* Title      : Read key without waiting
* Written by : Charles Kelly
* Date       : Dec-22-2016
* Description: Read a keypress from the keyboard without
*              waiting for input.
*-----------------------------------------------------------
    ORG    $1000
START:                  ; first instruction of program

* Put program code here
    clr.l   count       ; count = 0
Loop
    add.l   #1,count    ; count = count + 1
    move.b  #7,D0       ; Task 7, Check for keyboard input. Set D1.B to 1 if keyboard input is pending,
                        ; otherwise set to 0. Use task 5 to read pending key.
    trap    #15
    if.b D1 <eq> #1 then.s    ; if keyboard input pending
        move.b  #5,D0   ; Task 5, Read single ASCII character from the keyboard into D1.B.
        trap    #15
        move.l  count,D1    ; get count value
        move.b  #3,D0   ; Task 6, Display number in D1.L
        trap    #15     ; Display loop count
    endi
    bra loop
    

    SIMHALT             ; halt simulator

* Put variables and constants here
count   ds.l    1       ; loop counter
    END    START        ; last line of source

_________________
Prof. Kelly

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JimL

Post subject: Re: Terminating a loop

Posted: Thu Dec 22, 2016 9:40 pm

Joined: Thu Dec 22, 2016 5:21 pm
Posts: 2

profkelly, that was a great help.

Thanks.

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