83Plus:Ports:3A
From WikiTI
| This port only exists as a distinct port on the TI-83 Plus Silver Edition, the TI-84 Plus, and the TI-84 Plus Silver Edition. On the standard TI-83 Plus, it acts as a shadow of port 02. |
Contents
Synopsis
Port Number: 3Ah
Function: GPIO
This port appears to be for GPIO reading/writing. It's used for USB stuff, battery voltage testing, and on the TI-84+CSE, controlling the backlight. Port 39h appears to be the GPIO setup register. More work is needed to figure out what hardware these GPIO pins interface with.
Old hardware
Read Values
- Bits 0-2 - Used for USB related stuff
- Bit 3 - Set
- Bits 4-7 - Unknown
Write Values
- Bits 0-2 - Used for USB related stuff
- Bit 3 - No effect
- Bit 4 - Set after using port 04 to check batteries but then reset
- Bits 5-6 - Unknown
- Bit 7 - Set before using port 04 to check batteries
New Hardware
Read Values
- Bits 0-3 - Reset
- Bits 4-7 - No significance
Write Values
- Bits 0-3 - Unchangeable
- Bits 4-7 - Quirky (no effect)
Comments
The purpose of the lower 3 bits is unknown. Someone with a model (none) or A calculator will have to do some testing. If the old USB hardware is present, most of the USB ports work differently.
On the old hardware, port 39h also seems to be tied to the functions of this port.
Another way to check for the old USB revision is to check port 15h for the value 44h.
