83Plus:Ports:03

Synopsis

Port Number: 03h

Function: Interrupt Masking Port

This port controls what devices will be allowed to trigger interrupts. When an interrupt is triggered, it should be cleared by reseting the corresponding bit. Otherwise, it will continously call the interrupt code once interrupts are reenabled with ei.

Read Values

• Bit 0: Set if pressing the ON key will generate an interrupt.
• Bit 1: Set if the first hardware timer will generate an interrupt (range: 108Hz-512Hz).
• Bit 2: Set if the second hardware timer will generate an interrupt (range: 216Hz-1024Hz).
• Bit 4: Set if the linkport will generate an interrupt.

Write Values

• Bit 0: Set 1 to enable the ON key. Set 0 to disable it.
• Bit 1: Set 1 to enable the first hardware timer. Set 0 to disable it.
• Bit 2: Set 1 to enable the second hardware timer. Set 0 to disable it.
• Bit 3: Set 0 to put the calculator in low power mode if and only if the Z80 cpu enters the halt state (during the executing of a halt instruction). Set 1 to keep the calculator powered.
• Bit 4: Set 1 to enable the linkport interrupt. Set 0 to disable it. (Does not completely disable the linkport.)

Comments

• For normal operation, write 0B (00001011) to this port.
• In low power mode it is known that at least the lcd driver enters standby mode and that the timer hardware has been disabled.

Example

This example shows how to do a soft powerdown (similar to the auto powerdown) on the calculator. This may or may not wipe the LCD screen, so you should first copy it's contents to a buffer like saveSScreen and then copy it back afterwards.

 push af
 ld a, 11h ;Enable linkport, ON key. Disable timer.
           ;Set low power mode.
 out (3), a
 halt      ;Enter low power mode (disabling various devices)
           ;and wait for an interrupt (either ON key or
           ;link activity) which will enable all hardware
           ;devices again.
 ld a, 0Bh ;Enable ON key, timer. Disable linkport.
           ;Keep calculator powered.
 out (3), a
 pop af

Credits and Contributions

• Michael Vincent: For documenting here on the interrupt bits.
• James Montelongo: For documenting here on the interrupt bits.