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Elite on the BBC Micro

Keyboard: TT217 [Elite-A, Parasite]

Name: TT217 [Show more] Type: Subroutine Category: Keyboard Summary: Scan the keyboard until a key is pressed by sending a get_key command to the I/O processor
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * gnum calls TT217 * qv calls TT217 * DK4 calls entry point out

Scan the keyboard until a key is pressed, and return the key's ASCII code. If, on entry, a key is already being held down, then wait until that key is released first (so this routine detects the first key down event following the subroutine call). Returns: X The ASCII code of the key that was pressed A Contains the same as X Other entry points: out Contains an RTS
.TT217 .t LDA #&8D \ Send command &8D to the I/O processor: JSR tube_write \ \ =get_key() \ \ which waits for any current key presses to be released \ (if any), and then waits for a key to be pressed \ before returning the result as an ASCII value JSR tube_read \ Set A to the response from the I/O processor, which \ will contain the ASCII value of the key press TAX \ Copy the response into X .out RTS \ Return from the subroutine