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Elite on the BBC Micro

Keyboard: U%

[BBC Master version]

Name: U% [Show more] Type: Subroutine Category: Keyboard Summary: Clear the key logger
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: * BR1 (Part 1 of 2) calls U% * RDKEY2 calls U% * TITLE calls U%

Returns: A A is set to 0 X X is set to 0
.U% LDA #0 \ Set A to 0, as this means "key not pressed" in the \ key logger at KL LDX #17 \ We want to clear the 17 key logger locations from \ KL to KY20, so set a counter in Y .DKL3 STA JSTY,X \ Store 0 in the Y-th byte of the key logger DEX \ Decrement the counter BNE DKL3 \ And loop back for the next key, until we have just \ KL+1. We don't want to clear the first key logger \ location at KL, as the keyboard table at KYTB starts \ with offset 1, not 0, so KL is not technically part of \ the key logger (it's actually used for logging keys \ that don't appear in the keyboard table, and which \ therefore don't use the key logger) RTS \ Return from the subroutine