Differences

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--- documentations:devices:6821 [2014/03/26 21:27] – [TO System PIA] pulkomandy
+++ documentations:devices:6821 [2018/08/17 09:08] – [MO System PIA] pulkomandy
@@ Line 12: / Line 12: @@
 The control registers have the following functions:
-=== Bit 7: interrpupt pin 1 state ===
+=== Bit 7: interrput pin 1 state ===
 This bit is set on transition (low>high or high>low) of the CA1 or CB1 pin. It is cleared by reading the output register.
-=== Bit 6: interrpupt pin 2 state ===
+=== Bit 6: interrput pin 2 state ===
 This works the same as bit 7, but is only used when CA2 or CB2 is configured as an input pin. Otherwise, the pin can't be used as an interrupt source.
@@ Line 43: / Line 43: @@
 ===== Uses =====
 ==== MO "System" PIA ====
-=== data port A ===
+=== data port A (A7C0) ===
   * bit 0: /FORME - Switch the screen RAM mapping between pixel and attribute RAMs
   * bits 1-4: border color (R,G,B,P)
@@ Line 50: / Line 50: @@
   * bit 7: tape drive data input
-Bit 7 is low when no tape drive is plugged, and high when there is one. The monitor loading and saving code checks for this to detect the ape drive.
+Bit 7 is low when no tape drive is plugged, and high when there is one. The monitor loading and saving code checks for this to detect the tape drive.
-=== data port B ===
+=== data port B (A7C1) ===
   * bit 0: sound output
   * bits 1-3: keyboard column to scan
@@ Line 58: / Line 58: @@
   * bit 7: state of key selected by the column and line
-=== Control ports ===
+=== Control ports (A7C2, A7C3) ===
   * CA1: lightpen interrupt (IRQA is wired to 6809 FIRQ)
   * CA2: tape drive motor control (output)
@@ Line 119: / Line 119: @@
 ==== "Sound and Games" PIA ====
+Available as an expansion for the TO7, TO7/70, TO9 and MO5, this is built-in for the other machines.
+<columns>
 === Data port A ===
-  * Joystick reading
+^Bit^Joystick 0 ^Mouse       ^Joystick 1^
+|PA0|Up         |Left click  | |
+|PA1|Down       |Right click | |
+|PA2|Left       |XB          | |
+|PA3|Right      |YB          | |
+|PA4| | |Up   |
+|PA5| | |Down |
+|PA6| | |Left |
+|PA7| | |Right|
+<newcolumn>
 === Data port B ===
-  * DAC output (6 bits)
-  * Player 2 action button
+^Bit^Joysticks      ^Mouse^Sound    ^
+|PB0|Common 0       |     |DAC bit 0|
+|PB1|Common 1       |     |DAC bit 1|
+|PB2|Joy0 button 2  |XA   |DAC bit 2|
+|PB3|Joy1 button 2  |     |DAC bit 3|
+|PB4| | |DAC bit 4|
+|PB5| | |DAC bit 5|
+|PB6|Joy0 button 1  |YA | |
+|PB7|Joy1 button 1  | | |
+</columns>
 === Control ports ===
-  * CA1: player 1 action button
+The joystick buttons are wired both to port input pins and to control pins. This makes it possible to trigger interrupts on them, but read the complete joystick state for both joysticks on data ports A and B without having to also test the control ports.
-  * CB1: player 2 action button
+  * CA1: Joy0 button 2
+  * CA2: Joy0 button 1
+  * CB1: Joy1 button 2
+  * CB2: Joy1 button 1
+It is not possible to use the DAC and the joysticks (or the mouse) at the same time! This is particularly annoying for the mouse, as one of the quadrature encoded signals will interfere with the DAC. So you have to move the mouse very slowly until it is not interfering anymore. Or, you can unplug the mouse when it is not in use.
+The sound output from the DAC can be muted by using the 6846 buzzer output to force it low. Or, the DAC cn be used as a "volume control" for the buzzer, because of the way they are mixed together.
 ===== Documents =====
   * {{:documentations:devices:pia_6821.pdf|Datasheet}}