Micropower

RESET (D,E)
8007	CD1680	RESET	CALL CSPOS	Calculate screen posn.
800A	CD58FF		CALL BRESET	Use Basic ROM
800D	C9 RET
		All registers corrupted (except alternate set)

POINT (D,E)
800E		POINT	CALL CSPOS	Calculate screen posn.
8011	46		LD B, (HL)	Pick up char. on screen
8012	CDEDFF		CALL BPOINT	Use Basic ROM
8015	C9		RET
		NZ if point set, Z if reset All registers corrupted (except alternate set)

CALCULATE SCREEN POSITION
8016	6A	CSPOS	LD L, D	Low byte of x co-ord
8017	2600		LD H, 0	High byte set to zero
8019	E5		PUSH HL	Put on stack for ROM
801A	1600		LD D, 0	Set high of y to zero
801C	C331FF		JP BCSPOS	Basic ROM does rest

		On exit	HL = Screen Address
			A = Pixel information
		All other registers corrupted

CHECK CO-ORDS AREWITHIN RANGE AND CONVERT THE Y CO-ORDS SO (0,0) IS AT THE BOTTOM LEFT CORNER
801F	7A	CHECK	LD A, D	X Co-ordinate
8020	FE60		CP 96	Screen width
8022	3F		CCF
8023	D8		RET C	End if D > 95
8024	7B		LD A, E	Y co-ordinate
8025	FE30		CP 48	Screenheight
8027	3F		CCF
8028	D8		RET C	End if E > 47
8029	FE2D		CP 45
802B	3005		JR NC,CH2	Jump if 44 < E < 48
802D	3E2C		LD A, 44
802F	93		SUB E	Carry will not be set
8030	5F		LD E, A	New y co-ord in E
8031	C9		RET
8032	3E5C	CH2	LD A, 92	Sort out top line
8034	93		SUB E	Carry will not be set
8035	5F		LD E, A	Carry will not be set
8036	C9		RET
		On exit D and E contain new co-ords. Carry set if out of range

Volume 1 · Number 2 · September 1981