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Elite on the BBC Micro

Keyboard: DODKS4 [6502SP version, I/O processor]

Name: DODKS4 [Show more] Type: Subroutine Category: Keyboard Summary: Implement the #DODKS4 command (scan the keyboard to see if a specific key is being pressed)
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * OSWVECS calls DODKS4

This routine is run when the parasite sends a #DODKS4 command with parameters in the block at OSSC(1 0). It scans the keyboard to see if the specified key is being pressed. Arguments: OSSC(1 0) A parameter block as follows: * Byte #2 = The internal number of the key to check See p.142 of the Advanced User Guide for a list of internal key numbers Returns: OSSC(1 0) A parameter block as follows: * Byte #2 = If the key is being pressed, it contains the original key number from byte #2, but with bit 7 set (i.e. key number + 128). If the key is not being pressed, it contains the unchanged key number
.DODKS4 LDY #2 \ Fetch byte #2 from the block pointed to by OSSC, which LDA (OSSC),Y \ contains the key to check, and store it in A DKS4 \ Include macro DKS4 to check whether the key in A is \ being pressed, and if it is, set bit 7 of A STA (OSSC),Y \ Store the updated A in byte #2 of the block pointed to \ by OSSC RTS \ Return from the subroutine