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This port only exists on the the TI-84 Plus and the TI-84 Plus Silver Edition. On the standard TI-83 Plus, it acts as a shadow of port 04. On the TI-83 Plus Silver Edition, this port has no effect.


Port Number: 54h

Function: USB Controller Control

This port controls the USB controller. It is closely tied to port 4C


  • Bit 0: Set to enable USB suspend interrupt. You should turn off USB stuff when you get this interrupt.
  • Bit 1: USB controller disable. Setting this disables the 48 MHz crystal. Resetting causes a 5.67 mA increase in draw.
  • Bit 2: Manually enables USB controller. Setting this also sets 4, port 4C. This along with 3, port port 4C turn the 80-AF ports on. Causes a 1.15 mA increase in draw.
  • Bit 3: Read-only. Something to do with enabling the 48 MHz crystal.
  • Bit 4: If set, the hardware will automatically turn itself off when appropriate.
  • Bit 5: Read-only. Tells you whether the controller has automatically turned itself off.
  • Bit 6: 5, port 4C is the inverse of this. Must be set to do USB stuff. Causes a 0.22 mA increase in draw.
  • Bit 7: Setting this also sets 6, port 4C. Must be set to do USB stuff. Something to do with the charge pump.


Under normal conditions, you would output C4h to this port to use USB. When you are done, output 02h or suffer serious battery usage.

If 3, port 3A is set. You should first output 44h to this then follow it with C4h to use USB.