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documentations:devices:6821 [2014/03/26 21:27] – [TO System PIA] pulkomandydocumentations:devices:6821 [2018/08/17 09:10] (current) pulkomandy
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 The control registers have the following functions: 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. 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. 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.
  
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 ===== Uses ===== ===== Uses =====
 ==== MO "System" PIA ==== ==== MO "System" PIA ====
-=== data port A ===+=== data port A (A7C0) ===
   * bit 0: /FORME - Switch the screen RAM mapping between pixel and attribute RAMs   * bit 0: /FORME - Switch the screen RAM mapping between pixel and attribute RAMs
   * bits 1-4: border color (R,G,B,P)   * bits 1-4: border color (R,G,B,P)
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   * bit 7: tape drive data input   * 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   * bit 0: sound output
   * bits 1-3: keyboard column to scan   * bits 1-3: keyboard column to scan
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   * bit 7: state of key selected by the column and line   * 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)   * CA1: lightpen interrupt (IRQA is wired to 6809 FIRQ)
   * CA2: tape drive motor control (output)   * CA2: tape drive motor control (output)
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 ==== TO "System" PIA ==== ==== TO "System" PIA ====
  
-=== Data port A ===+=== Data port A (E7C8) ===
  
 == PA0: KTEST == == PA0: KTEST ==
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 These bits are wired to printer port D1-D7. Bit 0 is PB0 (this would have been too simple!) These bits are wired to printer port D1-D7. Bit 0 is PB0 (this would have been too simple!)
  
-=== Data port B ===+=== Data port B (E7C9) ===
  
 == PB0-PB1: printer missing bits == == PB0-PB1: printer missing bits ==
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 Seriously, this system is a mess. Use the new banking from the gate array if you can. Seriously, this system is a mess. Use the new banking from the gate array if you can.
  
-=== Control port A ===+=== Control port A (E7CA) ===
 == CA1: video incrustation sync == == CA1: video incrustation sync ==
 This is connected to the video incrustation CLRG signal. The only use is detecting that the signal is available from software. This is useful, because switching the video incrustation on without this would crash the machine. This is connected to the video incrustation CLRG signal. The only use is detecting that the signal is available from software. This is useful, because switching the video incrustation on without this would crash the machine.
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 Triggered when the lightpen sensor detects the screen refresh. Triggered when the lightpen sensor detects the screen refresh.
  
-=== Control port B ===+=== Control port B (E7CB) ===
 ==== "Sound and Games" PIA ==== ==== "Sound and Games" PIA ====
  
 +Available as an expansion for the TO7, TO7/70, TO9 and MO5, this is built-in for the other machines.
  
-=== Data port A === +<columns>
-  * Joystick reading+
  
-=== Data port === +=== Data port A (x7CC) === 
-  * DAC output (6 bits) +^Bit^Joystick 0 ^Mouse       ^Joystick 1^ 
-  * Player 2 action button +|PA0|Up         |Left click  | | 
-=== Control ports === +|PA1|Down       |Right click | | 
-  * CA1: player 1 action button +|PA2|Left       |XB          | | 
-  * CB1: player 2 action button+|PA3|Right      |YB          | | 
 +|PA4| | |Up   | 
 +|PA5| | |Down | 
 +|PA6| | |Left | 
 +|PA7| | |Right|
  
 +<newcolumn>
 +
 +=== Data port B (x7CD) ===
 +
 +^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 (x7CE/x7CF) ===
 +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.
 +  * 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 ===== ===== Documents =====
   * {{:documentations:devices:pia_6821.pdf|Datasheet}}   * {{:documentations:devices:pia_6821.pdf|Datasheet}}
documentations/devices/6821.1395865642.txt.gz · Last modified: 2015/02/28 18:08 (external edit)
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