83Plus:Ports:4C

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.

Synopsis

Port Number: 4Ch

Function: USB Controller Status

This port seems to be a status port for the USB controller. It is closely tied with port 54. If the USB controller is not powered, this port will always read either 22h or 2Ah depending on what was last written to bit 3.

Read Values

• Bit 0: Should be set if USB bus is in suspended state?
• Bit 1: Reset when a USB reset signal comes from the host
• Bit 2: Probably chirps at the start of each USB frame.
• Bit 3: Something to do with OTG and reset. This bit is only significant if 2, port 54 is set. If set, the 80-AF ports are active. Causes a 0.19 mA increase in draw.
• Bit 4: Reflection of 2, port 54.
• Bit 5: Inverse of 6, port 54.
• Bit 6: Reflection of 7, port 54.
• Bit 7: No function

Write Values

• Bits 0-2: Read-only
• Bit 3: Something to do with OTG and reset. If 2, port 54 is also set. This enables the 80-AF ports. Causes a 0.19 mA increase in draw.
• Bits 4-6: Read-only
• Bit 7: No function

Comments

USB initialization should only be attempted if this port reads 5Ah or 1Ah. In reality though, 1Ah is only used if 3, port 3A is set, so 5Ah is the value you are looking for.