Difference between revisions of "83:Ports:03"

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'''Function:''' Interrupt Control Port
 
'''Function:''' Interrupt Control Port
  
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This port has two modes. During normal program flow it indicates what devices are allowed to generate an interrupt. During an interrupt it indicates what device generated the interrupt.
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This port controls all devices that can generate interrupts.
  
 
=== Read Values ===
 
=== Read Values ===
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* Bit 0:
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* Bit 0: Set if the ON key generated an interrupt.
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** Normal mode: Always 0.
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* Bit 1: Set if the first hardware timer generated an interrupt.
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** Interrupt mode: Set if the ON key generated an interrupt.
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* Bit 2: Set if the second hardware timer generated an interrupt.
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* Bit 1:
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** Normal mode: Always 0.
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** Interrupt mode: Set if the first hardware timer generated an interrupt.
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* Bit 2:
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** Normal mode: Always 0.
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** Interrupt mode: Set if the second hardware timer generated an interrupt.
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* Bit 3: Reset if the ON key is being pressed; set otherwise.
 
* Bit 3: Reset if the ON key is being pressed; set otherwise.
 
* Bit 4-7: Unused.
 
* Bit 4-7: Unused.
  
 
=== Write Values ===
 
=== Write Values ===
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* Bit 0:
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* Bit 0: Set 0 to disable ON key interrupts and to acknowledge an ON key interrupt. Set 1 to enable ON key interrupts.
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** Normal mode: Set 1 to enable the ON key interrupt. Set 0 to disable it.
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* Bit 1: Set 0 to disable interrupts from the first timer and to acknowledge an interrupt from the first timer. Set 1 to enable interrupts from the first timer.
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** Interrupt mode: Set 0 if you handled the ON key interrupt. Set 1 if you did not. If the ON key was one of the devices that triggered an interrupt, a new interrupt will then be generated immediately after you enable interrupts (EI) again.
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* Bit 2: Set 0 to disable interrupts from the second timer and to acknowledge an interrupt from the second timer. Set 1 to enable interrupts from the second timer.
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* Bit 1:
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* Bit 3: Set 0 to turn off the LCD. Set 1 to enable the LCD.
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** Normal mode: Set 1 to enable the first hardware timer. Set 0 to disable it.
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** Interrupt mode: Set 0 if you handled the first timer interrupt. Set 1 if you did not. If the first timer was one of the devices that triggered an interrupt, a new interrupt will then be generated immediately after you enable interrupts (EI) again.
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* Bit 2:
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** Normal mode: Set 1 to enable the second hardware timer. Set 0 to disable it.
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** Interrupt mode: Set 0 if you handled the second timer interrupt. Set 1 if you did not. If the second timer was one of the devices that triggered an interrupt, a new interrupt will then be generated immediately after you enable interrupts (EI) again.
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* Bit 3: Set 1 to enable the LCD. Set 0 to turn off the LCD.
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* Bit 4-7: Unused.
 
* Bit 4-7: Unused.
  
 
== Comments ==
 
== Comments ==
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When in interrupt mode, the port will return to normal mode after the first write, so after that you can set a proper interrupt mask from within your interrupt routine if you want.
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* Outside an interrupt routine, this port always reads either 00h or 08h.
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* You need to acknowledge interrupts. Otherwise a new interrupt will be generated directly after you enable interrupts again with EI. Because that disables that particular interrupt at the same time, you may have to write a second value to this port to reenable it.

Revision as of 12:54, 2 April 2005

Synopsis

Port Number: 03h

Function: Interrupt Control Port

This port controls all devices that can generate interrupts.

Read Values

  • Bit 0: Set if the ON key generated an interrupt.
  • Bit 1: Set if the first hardware timer generated an interrupt.
  • Bit 2: Set if the second hardware timer generated an interrupt.
  • Bit 3: Reset if the ON key is being pressed; set otherwise.
  • Bit 4-7: Unused.

Write Values

  • Bit 0: Set 0 to disable ON key interrupts and to acknowledge an ON key interrupt. Set 1 to enable ON key interrupts.
  • Bit 1: Set 0 to disable interrupts from the first timer and to acknowledge an interrupt from the first timer. Set 1 to enable interrupts from the first timer.
  • Bit 2: Set 0 to disable interrupts from the second timer and to acknowledge an interrupt from the second timer. Set 1 to enable interrupts from the second timer.
  • Bit 3: Set 0 to turn off the LCD. Set 1 to enable the LCD.
  • Bit 4-7: Unused.

Comments

  • Outside an interrupt routine, this port always reads either 00h or 08h.
  • You need to acknowledge interrupts. Otherwise a new interrupt will be generated directly after you enable interrupts again with EI. Because that disables that particular interrupt at the same time, you may have to write a second value to this port to reenable it.
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