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--- base:detect_pal_ntsc [2015-04-17 04:31] – external edit 127.0.0.1
+++ base:detect_pal_ntsc [2016-09-27 17:49] – sokrates
@@ Line 62: / Line 62: @@
 EDIT: This check assumes that the machine is not a Drean PAL-N, which has 312 lines and 65 cycles per line.
+===== Sokrates' variant =====
+Graham's variant with additional Drean PAL-N detection. First count rasterlines, then count cycles to differ between PAL and PAL-N:
+<code>
+    LDX #$00
+w0  LDA $D012
+w1  CMP $D012
+    BEQ w1
+    BMI w0
+    AND #$03
+    CMP #$03
+    BNE detectionDone ; done for NTSC
+    TAY
+countCycles
+    INX
+    LDA $D012
+    BPL countCycles
+    CPX #$5E  ; VICE values: PAL-N=$6C PAL=$50
+	      ; so choose middle value $5E for check
+    BCC isPAL
+    INY ; is PAL-N
+isPAL
+    TYA
+detectionDone
+    ...
+</code>
+Results in the accumulator:
+<code>
+#$01: 262 rasterlines and 64 cycles per line [NTSC: 6567R56A VIC] (OLD NTSC)
+#$02: 263 rasterlines and 65 cycles per line [NTSC: 6567R8 VIC]
+#$03: 312 rasterlines and 63 cycles per line [PAL: 6569 VIC]
+#$04: 312 rasterlines and 65 cycles per line [Drean PAL-N: 6572 VIC]
+</code>
 ===== TLR's more advanced variant =====