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Forums > C64 Coding > 1541 low level programming problem
2007-08-21 19:04
Peiselulli

Registered: Oct 2006
Posts: 81
1541 low level programming problem

Hello,
I have a problem that I don't understand. I tried the
following code for the 1541 :

    jsr $F97E       ; MOTOR_ON
    jsr $fe00       ; SET_READ_MODE
loop
    BIT $1C00       ; SYNC signal
    BMI loop        ; not yet found?
    LDA $1C01       ; read byte
    lda $1c00
    eor #$08
    sta $1c00
    CLV
-
    bvc -
    lda $1c01
    jmp loop


I expect (if a floppy is inserted) that the LED flickers, but it does not. If I remove the "bvc" command, it works like expected. Has anybody a idea what I have forgotten to initialize ?

 
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2007-08-22 19:11
Peiselulli

Registered: Oct 2006
Posts: 81
yes, it did.
is there something to initalize that i have forgotten ?
2007-08-22 19:14
Krill

Registered: Apr 2002
Posts: 2980
Also from my loader:
            lda #CB2_OUTPUT_HIGH | CB1_IRQ_ON_NEG_ACTIVE_EDGE | CA2_OUTPUT_HIGH | CA1_IRQ_ON_NEG_ACTIVE_EDGE
            sta VIA2_PCR

This is an lda #$ee sta $1c0c, maybe that fixes it?
2007-08-22 19:16
Peiselulli

Registered: Oct 2006
Posts: 81
many thanks, that was missing !
now it flickers :->
2007-08-22 19:21
Krill

Registered: Apr 2002
Posts: 2980
Greatness :)
2007-08-22 23:21
Graham
Account closed

Registered: Dec 2002
Posts: 990
Also, I'd add a wait loop after turning the motor on. It takes some time until it has 100% speed.

Oh and for searching a sync, you can use the routine at $F556.
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