2068 Peculiarities

I discovered something very peculiar about the 2068 when I tried to put some machine code into the area of memory normally occupied by the RAM-resident code “function dispatcher”. It seems as if machine code routines in this area (6200 hex or greater) run more slowly than identical rountines elsewhere in memory.

To see this for yourself, try putting the routine shown below at two locations: at A000 and at 6200, then run the two routines. Enter the routine at A000, save it to tape, then compare the results of the two sequences.

LOAD "" CODE 40960
PRINT USR 40960

LOAD "" CODE 25088
PRINT USR 25088

Machine code routine

A000	FE		DI
A001	3E02		LD A,02
A003	47		LD B,A
A004	21FF1F		LD HL,1FFF
A007	10FE	LOOP    DJNZ,LOOP
A009	De3FE		OUT (FE),A
A00B	EE0F		XOR 0F
A00D	06A4		LD B,A4
A00F	2D		DEC L
A010	20F5		JR NZ,LOOP
A012	05		DEC B
A013	20F5		DEC H
A014	20F1		JR NZ,LOOP
A016	FB		EI
A017	C9		RET