10 .TITLE"KEY MASK 1.0"¢20 ;********************************¢30 ;*** KEY MASK 1.0 ***¢40 ;***(c) 1982 by, Matt Loveless***¢50 ;*** written especially for ***¢60 ;*** ANTIC magazine ***¢70 ;********************************¢80 ;¢90 ;*** EQUATES ***¢0100 ;¢0110 KBCODE = $D209 ; Key board code¢0120 VKEYBD = $0208 ; Keyboard IRQ ve¢0130 TABLE = $CB ; Free zero Page locations¢0140 ;¢0150 ;=========================================================¢0160 ; INIT ROUTINE: Puts my keyboard handler online¢0170 ;=========================================================¢0180 *= $0600 ; Page 6¢0190 BEGIN SEI ; Disable IRQ's¢0200 LDA VKEYBD ; Point the keyboard vector to my¢0210 STA JMPLOC+1 ; routine, and set my routine's JMP¢0220 LDA VKEYBD+1 ; instruction to point to the OS's¢0230 STA JMPLOC+2 ; routine¢0240 LDA #MYRTN&255 ; Lo byte of my routine¢0250 STA VKEYBD¢0260 LDA #MYRTN/256 ; Hi byte of my routine¢0270 STA VKEYBD+l¢0280 PLA ; Remove USR amount byte¢0290 PLA ; Get hi byte of the mask string¢0300 STA TABLE+1¢0310 PLA ; Get lo byte¢0320 STA TABLE¢0330 CLI ; Re-Enable IRO's !¢0340 RTS ; Return to BASIC¢0350 ;=========================================================¢0360 ;THE NEW KEYBOARD INTERRUPT ROUTINE¢0370 ;=========================================================¢0380 MYRTN TYA ; Keyboard IRQ vector points here¢0390 PHA ; Save Y-register¢0400 LDY KBCODE ; Get the key code¢0410 LDA (TABLE),Y ; and use it to index into the string¢0420 BNE GONORM ; Is it masked out?¢0430 PLA ; YES - then ignore key and¢0440 TAY ; restore registers¢0450 PLA¢0460 RTI ; Exit the keyboard interrupt¢0470 ;¢0480 GONORM PLA ; Restore Y-register¢0490 TAY¢0500 JMPLOC JMP $0000 ; Go to normal system keyboard routine¢0510 .END¢
