84PCE:Ports:000D

Synopsis

Port Number: 000D

Function: Power control

Details

This port enables power to various parts of the ASIC. Each region reads as 0 when unpowered.

Bit [0]

USB controller power. Resets when unpowered. Returning to the OS without reinitializing causes it to freeze while USB is connected.

Bit [1]

LCD controller power. Resets when unpowered. The LCD does not update until the controller is initialized properly.

Bit [2]

Power for RAM range D20000-D3FFFF. When unpowered, its content is quickly randomized.

Bit [3]

Power for VRAM range D40000-D7FFFF. When unpowered, its content is quickly randomized.

Bits [4:7]

Writes have no effect. These bits read as 1 if the subsystems controlled by the corresponding bits in 0-3 are receiving power. There is a slight delay between changing bits 0-3 & these changing in response.