Port A is 8 bits wide and can be set for either input or output. It is used to interface to various hand-held controllers. Access to the controller is through SWCHA. The direction of data (input or output) must be set for each bit of the port, using the port's data direction register (DDR) SWACNT.
SWCHA (Port A, Joysticks/Paddles/Controllers)
| Name | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0
| |
| $282 | SWCHA | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
Joysticks
Two joysticks can be read by configuring the entire port as input (see SWACNT) and reading the data at SWCHA according to the following table
Direction | Player #
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D7 | 0 = RIGHT pressed | Player 0
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D6 | 0 = LEFT pressed | Player 0
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D5 | 0 = DOWN pressed | Player 0
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D4 | 0 = UP pressed | Player 0
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D3 | 0 = RIGHT pressed | Player 1
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D2 | 0 = LEFT pressed | Player 1
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D1 | 0 = DOWN pressed | Player 1
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D0 | 0 = UP pressed | Player 1 | |||||||
(Player 0 = left player, Player 1 = right player)
A "0" in a data bit indicates the joystick has been moved to close that switch.
All "1's" in a player's nibble indicates that joystick is not moving.