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--- base:detecting_sid_type_-_safe_method [2015-06-12 20:59] – groepaz
+++ base:detecting_sid_type_-_safe_method [2020-10-27 14:16] – silverdr
@@ Line 1: / Line 1: @@
+====== Detecting Sid Type - safe method ======
+This SID detection routine is based on the fact that there is a one cycle delay in the oscillator on 8580 compared to 6581 when turned on.
+<code>
+	;SID DETECTION ROUTINE
+	;By SounDemon - Based on a tip from Dag Lem.
+	;Put together by FTC after SounDemons instructions
+	;...and tested by Rambones and Jeff.
+	; - Don't run this routine on a badline
+	; - Won't work in VICE (always detects 6581) unless resid-fp emulation is enabled
+	sei		;No disturbing interrupts
+	lda #$ff
+	cmp $d012	;Don't run it on a badline.
+	bne *-3
+	;Detection itself starts here
+	lda #$ff	;Set frequency in voice 3 to $ffff
+	sta $d412	;...and set testbit (other bits don't matter) in VCREG3 ($d412) to disable oscillator
+	sta $d40e
+	sta $d40f
+	lda #$20	;Sawtooth wave and gatebit OFF to start oscillator again.
+	sta $d412
+	lda $d41b	;Accu now has different value depending on sid model (6581=3/8580=2)
+	lsr		;...that is: Carry flag is set for 6581, and clear for 8580.
+	bcc model_8580
+model_6581:
+	[...]
+model_8580:
+	[...]
+</code>