// Detect AC Frequency
    // ===================
    // PAL TEST 50Hz:   #$7f
    // PAL TEST 60Hz:   #$32
    // NTSC TEST 50Hz:  #$b3
    // NTSC TEST 60Hz:  #$70
    // NTSC2 TEST 50Hz: #$b3
    // NTSC2 TEST 60Hz: #$70
    // DREAN TEST 50Hz: #$70
    // DREAN TEST 60Hz: #$20

DetectACFrequency:
    lda #$ff
    sta $dc04
    sta $dc05              // CIA #1 Timer A = #$ffff
    sta $dc06
    sta $dc07              // CIA #1 Timer B = #$ffff
    lda #$00
    sta $dc0b
    sta $dc0a
    sta $dc09
    sta $dc08              // CIA #1 TOD set to 00:00:00:00
    ldx #%10000001         // CIA #1 Timer A Start + TOD = 50 Hz
    lda VideoSystem
    beq !+                 // Branch if PAL (use 50Hz)
    cmp #$03
    beq !+                 // Branch if DREAN (use 50Hz)
    ldx #%00000001         // CIA #1 Timer A Start + TOD = 60 Hz (NTSC/NTSC2)
!:  ldy #%01000001         // CIA #1 Timer B Start + Sync with Timer A
    lda $dc08
!:  cmp $dc08
    beq !-                 // Wait untill TOD changes with 1/10 second
    stx $dc0e              // CIA #1 Timer A Start
    sty $dc0f              // CIA #1 Timer B Start
    lda $dc08
!:  cmp $dc08
    beq !-                 // Wait untill TOD changes with 1/10 second
    lda $dc05


    ldx VideoSystem
    beq PALorDREAN
    cpx #$03
    beq PALorDREAN
NTSCorNTSC2:
    cmp Table50Hz,x
    bne TOD50Hz
    jmp TOD60Hz

PALorDREAN:
    cmp Table50Hz,x
    bne TOD60Hz
TOD50Hz:
    lda #$81
    ldx #$80
    ldy #50
    jmp !+
TOD60Hz:
    lda #$01
    ldx #$00
    ldy #60
!:  sta $dc0e
    stx $dd0e  // Set correct frequency on TOD Clocks and initialize CIA #1 & #2 Control Register A
    sty ACMains
    rts

    //---------------------------------------------------------------------
    // DATA: 50/60 Hz Detection Table
    //
    // PAL/50   - #$fffe 7f 28 -  98.519 cycles => MPU Clock = 0,985 MHz
    // PAL/60   - #$fffe 32 24 - 118.235 cycles
    //
    // NTSC/50  - #$fffe b3 0f -  85.232 cycles
    // NTSC/60  - #$fffe 70 7d - 102.274 cycles => MPU Clock = 1,023 MHz
    //
    // NTSC2/50 - #$fffe b3 12 -  85.229 cycles
    // NTSC2/60 - #$fffe 70 6b - 102.292 cycles => MPU Clock = 1,023 MHz
    //
    // DREAN/50 - #$fffe 70 23 - 102.326 cycles => MPU Clock = 1,023 MHz
    // DREAN/60 - #$fffe 20 32 - 122.829 cycles

Table50Hz:  // Values to detect that 
    .byte $7f  // PAL
    .byte $70  // NTSC_OLD
    .byte $70  // NTSC
    .byte $70  // DREAN