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Elite on the BBC Micro

Keyboard: DKS4 [6502SP version]

Name: DKS4 [Show more] Type: Subroutine Category: Keyboard Summary: Scan for a particular key press by sending a #DODKS4 command to the I/O processor
Context: See this subroutine in context in the source code Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * TT17 calls DKS4

This routine sends a #DODKS4 command to the I/O processor to ask it to scan the keyboard, to see if the key specified in X is currently being pressed. Arguments: X The internal number of the key to check Returns: A If the key is being pressed, A contains the original key number in X but with bit 7 set (i.e. key number + 128). If the key is not being pressed, A contains the unchanged key number
.DKS4 STX DKS4pars+2 \ Store the key number in byte #2 of the parameter block \ below LDX #LO(DKS4pars) \ Set (Y X) to point to the parameter block below LDY #HI(DKS4pars) LDA #DODKS4 \ Send a #DODKS4 command to the I/O processor to check JSR OSWORD \ whether the key in byte #2 of the parameter block is \ being pressed LDA DKS4pars+2 \ Fetch the result from byte#2 of the parameter block, \ which will have bit 7 set if the key is being pressed RTS \ Return from the subroutine .DKS4pars EQUB 3 \ The number of bytes to transmit with this command EQUB 3 \ The number of bytes to receive with this command EQUB 0 \ The key number to check RTS \ End of the parameter block