Difference between revisions of "Keyboard"

Revision as of 09:27, 31 December 2019

Number	$**FE
Decimal
Short desc.	Series of specific ports that read keyboard key presses.
Bit Mask	%xxxx xxxx ---- ---0 where only one bit in x is 0
Readable	Yes
Writable	No
Subsystem	Input

Reads keys on the keyboard depending on the upper byte of the port number. The five keys are represented by bits 0-4 of the read byte, listed below with bit 4 first down to bit 0. A zero means that the key is pressed.

The top eight bits of the port address are active low signals that select one or more key rows for reading.

Port upper byte	Keys affected (row of keys)
$7F (bit 7)	B, N, M, Symbol Shift, Space
$BF (bit 6)	H, J, K, L, Enter
$DF (bit 5)	Y, U, I, O P
$EF (bit 4)	6, 7, 8, 9, 0
$F7 (bit 3)	5, 4, 3, 2, 1
$FB (bit 2)	T, R, E, W, Q
$FD (bit 1)	G, F, D, S, A
$FE (bit 0)	V, C, X, Z, Caps Shift

File:Speckeys.png

@@ Line 8: / Line 8: @@
 }}
 Reads keys on the keyboard depending on the upper byte of the port number. The five keys are represented by bits 0-4 of the read byte, listed below with bit 4 first down to bit 0. A zero means that the key is pressed.
+The top eight bits of the port address are active low signals that select one or more key rows for reading.
 {| class="wikitable"
-! Port upper byte !! Keys affected
+! Port upper byte !! Keys affected (row of keys)
 |-
-| $7F || B, N, M, Symbol Shift, Space
+| $7F (bit 7) || B, N, M, Symbol Shift, Space
 |-
-| $BF || H, J, K, L, Enter
+| $BF (bit 6) || H, J, K, L, Enter
 |-
-| $DF || Y, U, I, O P
+| $DF (bit 5) || Y, U, I, O P
 |-
-| $EF || 6, 7, 8, 9, 0
+| $EF (bit 4) || 6, 7, 8, 9, 0
 |-
-| $F7 || 5, 4, 3, 2, 1
+| $F7 (bit 3) || 5, 4, 3, 2, 1
 |-
-| $FB || T, R, E, W, Q
+| $FB (bit 2) || T, R, E, W, Q
 |-
-| $FD || G, F, D, S, A
+| $FD (bit 1) || G, F, D, S, A
 |-
-| $FE || V, C, X, Z, Caps Shift
+| $FE (bit 0) || V, C, X, Z, Caps Shift
 |}
 [[File:Speckeys.png]]