Routines
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46583: Read Keyboard Port
Used by the routines at PlayMusic_WaitKey, GameOver, WaitForKeyPress, GameMenu, ReadInterface2Joystick, ReadCursorJoystick, ReadKeyboard and PauseGame.
Reads some rows of the keyboard. The row selector is also written to port 253 (with the selector as the high byte of the address), which does nothing on a 48K Spectrum and is not part of any sound; the keyboard is read with the same selector straight afterwards.
Input
A Row selector (a bit which is reset selects the row)
Output
A Keys pressed, in bits 0 to 4 (a bit is set when a key is pressed)
F Zero flag set if no key is pressed
Write the selector, then read the keys.
ReadKeyboardPort 46583 OUT (253),A Put the half-row selector on the high byte of the address bus.
46585 IN A,(254) Read the rows of the keyboard.
46587 CPL Invert the bits so that the pressed keys are set.
46588 AND %00011111 Keep only bits 0 to 4.
46590 RET Return.
View the equivalent code in;
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