80-Bus News

  

May-June 1984, Volume 3, Issue 3











Page 28 of 51











Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    100

FF02 D5         LINTBF: PUSH    DE              ; Line length to BC
FF03 C1                 POP     BC
FF04 03                 INC     BC              ; Length +1
FF05 116110             LD      DE,BUFFER       ; Input buffer
FF08 E1                 POP     HL              ; Line start
FF09 C5                 PUSH    BC              ; Save length
FF0A EDB0               LDIR                    ; Move line to buffer
FF0C 3E00               LD      A,0
FF0E 12                 LD      (DE),A          ; Mark end of buffer with 00
FF0F C1                 POP     BC              ; Restore buffer length
FF10 41                 LD      B,C             ; Length returned in B
FF11 216010             LD      HL,BUFFER-1     ; Point to start of buffer-1
FF14 C9                 RET

FF15 CD90E6     GETXYA: CALL    CHKSYN          ; Make sure "(" follows
FF18 28                 DEFB    "("
FF19 CD41ED             CALL    GETNUM          ; Get a number
FF1C CD8BE9             CALL    DEINT           ; Get integer -32768 to 32767
FF1F D5                 PUSH    DE              ; Save "X"
FF20 CD90E6             CALL    CHKSYN          ; Make sure "," follows
FF23 2C                 DEFB    ","
FF24 CD41ED             CALL    GETNUM          ; Get a number
FF27 CD90E6             CALL    CHKSYN          ; Make sure ")" follows
FF2A 29                 DEFB    ")"
FF2B CD8BE9             CALL    DEINT           ; Get integer -32768 to 32767
FF2E E5                 PUSH    HL              ; Save code string address
FF2F FDE1               POP     IY              ; In IY
FF31 CD96FF             CALL    XYPOS           ; Address and bit mask
FF34 F5                 PUSH    AF              ; Save mask
FF35 CDC2FF             CALL    ADJCOL          ; Adjust column
FF38 CD11FE             CALL    SCRADR          ; Get VDU address
FF3B F1                 POP     AF              ; Restore bit mask
FF3C 06C0               LD      B,11000000B     ; Block graphics base
FF3E B0                 OR      B               ; Set bits 7 & 6
FF3F C9                 RET

FF40 CD15FF     SETB:   CALL    GETXYA          ; Get co-ords and VDU address
FF43 F5                 PUSH    AF              ; Save bit mask
FF44 7E                 LD      A,(HL)          ; Get character from screen
FF45 FEC0               CP      11000000B       ; Is it a block graphic?
FF47 D250FF             JP      NC,SETOR        ; Yes - OR new bit
FF4A F1                 POP     AF              ; Restore bit mask
FF4B 77         PUTBIT: LD      (HL),A          ; Put character on screen
FF4C FDE5       RESCSA: PUSH    IY              ; Restore code string address
FF4E E1                 POP     HL              ; From IY
FF4F C9                 RET

FF50 C1         SETOR:  POP     BC              ; Restore bit mask
FF51 B0                 OR      B               ; Merge the bits
FF52 C34BFF             JP      PUTBIT          ; Save on screen

Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    101

FF55 CD15FF     RESETB: CALL    GETXYA          ; Get co-ords and VDU address
FF58 F5                 PUSH    AF              ; Save bit mask
FF59 7E                 LD      A,(HL)          ; Get byte from screen
FF5A FEC0               CP      11000000B       ; Is it a block graphic?
FF5C DA75FF             JP      C,NORES         ; No - Leave it
FF5F 063F               LD      B,00111111B     ; Six bits per block
FF61 A0                 AND     B               ; Clear bits 7 & 6
FF62 C1                 POP     BC              ; Get bit mask
FF63 A0                 AND     B               ; Test for common bit
FF64 CA4CFF             JP      Z,RESCSA        ; None - Leave it
FF67 7E                 LD      A,(HL)          ; Get byte from screen
FF68 E63F               AND     00111111B       ; Isolate bit
FF6A A8                 XOR     B               ; Clear that bit
FF6B FEC0               CP      11000000B       ; Is it a graphic blank?
FF6D C24BFF             JP      NZ,PUTBIT       ; No - Save character
FF70 3E20               LD      A," "           ; Put a space there
FF72 C34BFF             JP      PUTBIT          ; Save the space

FF75 C1         NORES:  POP     BC              ; Drop bit mask
FF76 C34CFF             JP      RESCSA          ; Restore code string address

FF79 CD15FF     POINTB: CALL    GETXYA          ; Get co-ords and VDU address
FF7C 46                 LD      B,(HL)          ; Get character from screen
FF7D CDEDFF             CALL    TSTBIT          ; Test if bit is set
FF80 C291FF             JP      NZ,POINT0       ; Different - Return zero
FF83 3E00               LD      A,0
FF85 0601               LD      B,1             ; Integer AB = 1
FF87 E1         POINTX: POP     HL              ; Drop return
FF88 FDE5               PUSH    IY              ; PUSH code string address
FF8A 111DEE             LD      DE,RETNUM       ; To return a number
FF8D D5                 PUSH    DE              ; Save for return
FF8E C3F2F0             JP      ABPASS          ; Return integer AB

FF91 0600       POINT0: LD      B,0             ; Set zero
FF93 C387FF             JP      POINTX          ; Return value

FF96 C1         XYPOS:  POP     BC              ; Get return address
FF97 E1                 POP     HL              ; Get column
FF98 E5                 PUSH    HL              ; And re-save
FF99 C5                 PUSH    BC              ; Put back return address
FF9A 7D                 LD      A,L             ; Get column
FF9B 0601               LD      B,00000001B     ; 2 bits per character
FF9D A0                 AND     B               ; Odd or even bit
FF9E F5                 PUSH    AF              ; Save it
FF9F D5                 PUSH    DE              ; Get row
FFA0 E1                 POP     HL              ; to HL
FFA1 110000             LD      DE,0            ; Zero line count
FFA4 010300             LD      BC,3            ; 3 blocks per line
FFA7 23                 INC     HL
FFA8 ED42       DIV3LP: SBC     HL,BC           ; Subtract 3
FFAA 13                 INC     DE              ; Count the subtractions
FFAB CAB1FF             JP      Z,DIV3EX        ; Exactly - Exit
FFAE F2A8FF             JP      P,DIV3LP        ; More to do


This is an OCR’d version of the scanned page and likely contains recognition errors.











Page 28 of 51