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Port Number: 02h

Function: Calculator Status Information

This port reports various status information, including battery strength, LCD driver status, and calculator type.

Read Values

  • Bit 0: Set if the batteries are good. Reset if the batteries are low. The calculator will refuse to Garbage Collect or receive a FLASH App or OS when the batteries are low. The voltage cutoff can be configured in port 04.
  • 83+SE / 84+(SE) only: Bit 1: At 15MHz this bit resets for a set delay after a command or data is sent to the LCD, otherwise this bit is always set. The amount of delay is controlled by port 2F. On the TI-73, this bit is always reset (this is how you distinguish between the 73 and 83+ series hardware).
  • Bit 2: Set if Flash is currently unlocked.
  • 83+ only: Bits 3-5:
    • Bit 3: Last value written to port 05 bit 0
    • Bit 4: Last value written to port 05 bit 1
    • Bit 5: Last value written to port 05 bit 2
  • 84+(SE) only: Bit 5: Set for TI-84+ and TI-84+ SE calculators. Reset for TI-83+ and TI-83+ SE calculators. More specifically, this indicates if the calculator is USB-capable or not.
  • Bit 6: Indicates if Link Assist is available.
  • Bit 7: Reset for a TI-83+ Basic and TI-73. Set for everything else.

Write Values

TI-83+ (Non-SE)

No effect.

TI-83+SE, TI-84+, TI-84+SE, TI-84+CSE

  • Bit 0: Write a 0 to acknowledge the ON key interrupt; write 1 to leave the status of the ON key interrupt alone.
  • Bit 1: ACK HW timer 1
  • Bit 2: ACK HW timer 2
  • Bit 3: Ignored
  • Bit 4: ACK Linkport
  • Bits 5-7: Ignored


See Port 21h for how to distinguish the 84+ Basic from the 84+ SE.


Battery checking

 push af
 in a, (2)
 and 01h
 call nz, BatteriesGood
 call z, BatteriesLow
 pop af

LCD Testing

 push af
 in a, (2)
 and 02h
 jr z, WaitLoop
 ;Send a command, like 03 (LCD "On").
 call LCDIsReady
 pop af

Device checking

This example also uses Port 21h.

 in a, (2)
 rlca ;Roll bit 7 into carry.
 jp nc, Regular83Plus
 and 40h ;Test bit 5, now rotated into bit 6.
 jp z, Silver83Plus
 in a, (21h)
 and 03h
 jp z, Regular84Plus
 jp nz, Silver84Plus

Credits and Contributions

  • Michael Vincent: Documentation of port 2 located here.