|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 05. On the TI-83 Plus Silver Edition, this port has no effect.|
Port Number: 4Dh
Function: USB Line State
This port reports the current states of the four functional USB lines.
- Bit 0: Reset if the D+ line is high or if 2 and 6 of port 54 are set, 3 of port 4C is set, and VBus is high.
- Bit 1: Set if the D+ line is high or if 2 and 6 of port 54 are set, 3 of port 4C is set, and VBus is high. (Cutoff for both between 1.5 V and 3 V)
- Bit 2: Set if the D− line is low.
- Bit 3: Set if the D− line is high. (Cutoff between 1.5 V and 3 V)
- Bit 4: Set if the ID line is low (i.e., a mini-A cable is connected.)
- Bit 5: Set if the ID line is high (i.e., no cable or a mini-B cable is connected.)
- Bit 6: Set if the Vbus line is high. Electricity actually has to be moving, it can't just be powered. (Cutoff between 3 and 4.5)
- Bit 7: Set if the Vbus line is low.
- No effect
This port allows you to see the actual states of the four (functional) USB lines at any given time. This is mainly useful for checking the states of the ID and Vbus lines; while USB is active, the D+ and D− lines will change far too rapidly for you to get any useful information by polling this port.
I haven't tested what the actual cutoff voltages are, or whether there's any hysteresis. There may be, but it's a good idea to be cautious anyway (e.g., if you're waiting for Vbus to go high, wait for a little while afterwards to be sure that it stays high.)