83:Ports:03

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.