;MEMCHK.CO by Paul Globman (c) 1988
;
;This is a non-destructive RAM test
;that tests all of RAM, including the
;locations where the program is loaded 
;to run.  It tests all bits in all RAM
;locations for reading and writing and
;will beep 5 times upon finding a bad
;RAM location.  If no problem RAM is 
;found, then 1 beep is sent.
;
;
RAMSTA:	equ A000H	;1st byte ram
ALTLCD:	equ 63574	;alt lcd buffer
BEEP:	equ 4F45H	;send beep
;
	org altlcd
	entry
;
	jmp memchk
MEMCH2:	lxi d,0		;end of RAM + 1
next2:	mov a,m		;HL=adrs tested
	mov b,a		;byte in B
	cma
	mov c,a		;complmnt in C
	mov m,a		;chnge RAM bits
	mov a,m		;look at byte
	cmp c		;bits chnge ok?
	mov m,b		;restore byte
	jnz bad		;no? error
	mov a,m		;look at byte
	cmp b		;bits chnge ok?
	jnz bad		;no? error
	inx h		;next address
	rst 3		;end of ram?
	jnz next2
	jmp done
;======================================
MEMCHK:	lxi d, memchk
	lxi h,ramsta
next:	mov a,m		;HL=adrs tested
	mov b,a		;byte in B
	cma
	mov c,a		;complmnt in C
	mov m,a		;chnge RAM bits
	mov a,m		;look at byte
	cmp c		;bits chnge ok?
	mov m,b		;restore byte
	jnz bad		;no? error
	mov a,m		;look at byte
	cmp b		;bits chnge ok?
	jnz bad		;no? error
	inx h		;next address
	rst 3		;memchk yet?
	jnz next
	jmp memch2
;======================================
bad:	call beep	;5 beeps means
	call beep	;bad ram...
	call beep
	call beep	;1 beep means
done:	jmp beep	;all is well
;
	end