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; --------------------------------------------------------------
; A program to read in a string of text and store it in RAM.
; The end of text will be labelled with ASCII code zero/null.
; --------------------------------------------------------------
; THE MAIN PROGRAM
MOV BL,70 ; [70] is the address where the text will
; be stored. The procedure uses this.
CALL 10 ; The procedure at [10] reads in text and
; places it starting from the address
; in BL.
; BL should still contain [70] here.
CALL 40 ; This procedure does nothing until you
; write it. It should display the text.
HALT ; DON'T USE END HERE BY MISTAKE.
; --------------------------------------------------------------
; A PROCEDURE TO READ IN THE TEXT
ORG 10 ; Code starts from address [10]
PUSH AL ; Save AL onto the stack
PUSH BL ; Save BL onto the stack
PUSHF ; Save the CPU flags onto the stack
Rep:
IN 00 ; Input from port 00 (keyboard)
CMP AL,0D ; Was key press the Enter key?
JZ Stop ; If yes then jump to Stop
MOV [BL],AL ; Copy keypress to RAM at position [BL]
INC BL ; BL points to the next location.
JMP Rep ; Jump back to get the next character
Stop:
MOV AL,0 ; This is the NULL end marker
MOV [BL],AL ; Copy NULL character to this position.
POPF ; Restore flags from the stack
POP BL ; Restore BL from the stack
POP AL ; Restore AL from the stack
RET ; Return from the procedure.
; --------------------------------------------------------------
; A PROCEDURE TO DISPLAY TEXT ON THE SIMULATED SCREEN
ORG 40 ; Code starts from address [10]
; **** YOU MUST FILL THIS GAP ****
RET ; At present this procedure does
; nothing other than return.
; --------------------------------------------------------------
END ; It is correct to use END at the end.
; --------------------------------------------------------------
TASK
17) Write a program using three procedures. The first should
read text from the keyboard and store it in RAM. The second
should convert any upper case characters in the stored text
to lower case. The third should display the text on the
VDU screen.
; --------------------------------------------------------------
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