Added GRAPHTST.ASM

src/GRAPHTST.ASM

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+; This is a simple test program for using escape sequences.
+; Defines some routines that send escape sequences to the terminal
+		ORG 100H         ; CP/M programs start at this address
+		JMP START        ; jump to the main entry point
+; Variable storage space
+MsgStr: DB 'Hello, world.',13,10,0
+ClsStr: DB 27,'[2J',0
+HmeStr: DB 27,'[H',0
+Stack:  DW 0             ; place to save the old stack
+SBOT:   DS 32            ; reserve a local stack
+; Constants
+STOP:   EQU $-1          ; top of our stack
+BDOS:   EQU 5            ; adress of the BDOS call 
+; Start of code
+; PRINTF: Prints a string on the screen using a BDOS function. 
+; The address of the string is expected to be in register HL.
+PRINTF:
+PRLOOP: MOV A, M         ; read next char
+		ORA A            ; check, if string has ended
+		JZ  PREND        ; if char == 0, then leave
+		MOV E, A         ; load the char into E
+		MVI C, 2         ; call BDOS function id 2
+		PUSH H           ; save the HL register
+		CALL BDOS        ; call the BDOS function
+		POP H            ; restore the HL register
+		INX H            ; point to the next char
+		JMP PRLOOP       ; do the next char
+PREND:  RET              ; return from subroutine
+; CLS: Clears the screen by printing an escape sequence
+CLS:    LXI H, ClsStr    ; Load the escape sequence
+		CALL PRINTF      ; print the sequence
+		RET              ; return
+; HOME: Places the cursor in the upper right corner.
+HOME:   LXI H, HmeStr    ; Load the escape sequence
+		CALL PRINTF      ; print the sequence
+		RET
+; Start of the main code block
+START:  LXI H, 0         ; blank out HL
+		DAD SP           ; HL = SP
+		SHLD Stack       ; save the original stack
+		LXI H, STOP      ; set HL to the new stack top
+		SPHL             ; set SP to point to our new stack
+		CALL CLS         ; clear the screen
+		CALL HOME        ; place cursor in the top left
+		LXI H, MsgStr    ; load the string addr into HL
+		CALL PRINTF      ; call our self defined print routine
+		LHLD Stack       ; load original stack addr into HL
+		SPHL             ; restore the original stack
+		RET              ; return control back to CP/M
+		END