A few simple programs to exercise the COSMAC Elf.

• Blinky Mem
• Walking Bit
• Q Toggle
• Tone Generator

Program:	Blinky Mem
Comment:	Scans through memory, displaying each byte with a delay for visibility.
		For suitably random memory contents, displays some suitably random blinking lights.
		Also blinks the Q LED as the scan passes through 0 mod 256.
Source:		bh (2011 Aug)

Registers:
0:  PC
1:  delay counter
2:  pointer into mem

Addr	Mem	Label	Instr		Comment
----	---	-------	---------------	---------------------------	
 0      E2      Start   SEX 2		X refs R2
 1      F8              LDI 0		0 -> R2
 2      00
 3      A2		PLO 2
 4      B2              PHI 2

 5	82	Loop	GLO 2		Check low bits of pointer
 6	CE		LSZ		for 0.
 7	7A		REQ		And display Q appropriately.
 8	38		SKP
 9	7B		SEQ
 A      64		OUT 4		Display mem, increment pointer.

 B      F8      delay	LDI 8		Delay is 256*num.
 C      08
 D      B1              PHI 1		Load delay into high bits.

 E      21      DlyLp	DEC 1		Count down
 F      91              GHI 1
10      3A              BNZ DlyLp	until 0.
11      0E

12      30              BR Loop		Loop for next mem location.
13      05

Program:	Walking Bit
Comment:	A simple blinky-light program to rotate a bit around the 8 display LEDs.
Source:		bh (2011 Aug)

Registers:
0:  PC
1:  delay counter
2:  pointer to bit pattern

Addr	Mem	Label	Instr		Comment
----	---	-------	---------------	---------------------------	
 0      E2      Start	SEX 2		X refs R2
 1      F8		LDI BitPtrn	R2 refs BitPtrn
 2      17
 3      A2		PLO 2
 4      F8		LDI 0
 5      00
 6      B2		PHI 2
 7      FD		SDI 0		Set DF to 1 to start bit pattern.
 8      00

 9      52      WalkLp	STR 2		Save bit pattern.
 A      64		OUT 4		Display bit pattern
 B      22		DEC 2		and undo increment from OUT.

 C      F8      delay	LDI 8		Delay is 256*num.
 D      08
 E      B1		PHI 1		Load delay into high bits.

 F      21      DlyLoop	DEC 1		Count down.
10      91		GHI 1
11      3A		BNZ DlyLoop	Loop until 0.
12      0F

13      02		LDN 2		Rotate BitPtrn
14      76		RSHR		to right.
15      30		BR WalkLp	Loop to display.
16      09

17       -	BitPtrn	-		the bit pattern

Program:	Q Toggle (Blink)
Comment:	Toggle the Q Bit and so blink the Q LED.
Source:		Popular Electronics Sep 1976 Elf article

Registers:
0:	PC				
1:	delay counter					
						
Addr	Mem	Label	Instr		Comment
----	---	-------	---------------	---------------------------	
 0	7A		REQ		Q off

 1	F8	Delay	LDI 16		Delay will be 256*num
 2	10
 3	B1		PHI 1		Load delay into high bits of R1

 4	21	DlyLoop	DEC 1		--R(1)
 5	91		GHI 1		R(1).1 -> D
 6	3A		BNZ DlyLoop	Loop until 0
 7	04

 8	31		BQ 0		If Q is on go turn it off.
 9	00
10	7B		SEQ		Turn Q on.
11	30		BR Delay	Go delay.
12	01

Program:	Tone Generator
Comment:	Toggles Q at a rate determined by the data switches.
		With Q connected appropriately to a speaker, tones of different frequencies will be generated.
Source:		bh (2011 Aug)

Registers:
0:  PC
1:  delay counter
2:  dummy pointer for IN

Addr	Mem	Label	Instr		Comment
----	---	-------	---------------	---------------------------	
 0      E2      Start   SEX 2		X refs R2.
 1      F8              LDI 0		Init R2 to point to dummy.
 2      00
 3      B2		PHI 2
 4	F8		LDI dummy	IN will need location to load into.
 5	12
 6      A2              PLO 2

 7	7A	QOff	REQ		Turn Q off.

 8      6C      Delay	IN 4		Get delay count from switches.
 9      FF	DelayLp	SMI 1		Count down
 A      01
 B      3A              BNZ DlyLp	until 0.
 C      09

 D	31		BQ QOff		If Q is on go turn it off.
 E	07
 F	7B		SEQ		Turn Q on.
10	30		BR Delay	Go delay.
11	08

12	-	dummy	-		Dummy location for IN.