84PCE:Ports:0000 Unknowns

If a port is not listed; it indicates that writes have no effect and do not latch, and that reads are 0. Note that this may not be true one hundred percent.

0000 Range

Port	Default	Bits	Information
0000	03	D3	CPU Speed Control
0001	03	13	OS Timer Control
0002		??	Read only, value can change
0005	76	??	Set bit 5 to freeze, bit 6 affects backlight
0006	03	03?	Display refresh
0007	B7	FF	Latches values written
0008	7F	7F	Cannot change value
0009		??	Appears to be a part of the power control system.
000A	05	??	Latches value written, OS reset to 05
000B	FC	??	Cannot change value
000C	00	FF	Latches value written
000D	FF	FF	Bit 0: Freeze if reset Bit 1: Crash if reset Bit 2: No apparent effect if reset Bit 3: Reset to disable VRAM? Upon set, VRAM is garbage. Bits [7:4]Possibly last value written
000E	0A	FF	Latches value written
000F	42	?3	High nibble may be a status, low 2 bits latch value written
001C	80	??	Cannot change value
0028		FD	Bit 1 is always 0, other bits latch value written
0029	00	01	Bit 0 latches value written
002A	70	73	Latches value written
002B	FE	FF	Latches value written
002C		FF	Ports 002C-0031 latch value written
0032		07	Latches value written
0033		F1	Latches value written
0034		31	Latches value written
0035		3F	Latches value written
0036		FF	Ports 0036-0039 latch value written