PIO port

PIO port

Background

Some versions of the PlayStation console have a port on the back labeled "Parallel I/O", pictured here:

The name can be confusing, as it's not an IEEE 1284 printer port, but a proprietary port from Sony, that shares a lot of similarities with the IBM PC ISA bus.

The port was present on all versions of the console, up until the SCPH-900x versions, that removed it.

There is a lot of documentation about this port available online, but this page will be repeating it for the sake of consistency and cross referencing.

Pinout

The 68 pins are labeled left to right first, then top to bottom, as pictured:

This pinout is written on the top silkscreen of the motherboard:

Some modifications exist to this PIO port that we will discuss in details. The pinout below takes the known modifications into account.

signal	number	number	signal	comment
GND	1	35	GND	These are strong ground signals, meant for power distribution
!RESET	2	36	DACK5
DREQ5	3	37	!IN10
!CS0	4	38	!SWR1
SBEN	5	39	!CS2	These are weak ground signals, that can easily be cut to add the SBEN and !CS2 signals
D0	6	40	D1
D2	7	41	D3
D4	8	42	D5
D6	9	43	D7
D8	10	44	D9
D10	11	45	D11
D12	12	46	D13
D14	13	47	D15
A0	14	48	A1
A2	15	49	A3
GND	16	50	GND	These are somewhat weak ground signals, but their proximity to power may be a bad idea to cut and reuse
3.3v	17	51	3.3v
8v	18	52	8v
GND	16	53	GND	These are somewhat weak ground signals, but their proximity to power may be a bad idea to cut and reuse
A4	17	54	A5
A6	18	55	A7
A8	19	56	A9
A10	20	57	A11
A12	21	58	A13
A14	22	59	A15
A16	23	60	A17
A18	24	61	A19
A20	25	62	A21
A22	26	63	A23
!SRD	30	64	!SWR0
!IN2	31	65	!CS5	These are non-connected signals, that are commonly reused to redirect the !IN2 and !CS5 signals
SYSCLK1	32	66	LRCLK
BCLK	33	67	SDIN
GND	34	68	GND	These are strong ground signals, meant for power distribution

Signals signification

The architecture of the PSX busses are really similar to that of the ISA bus, and thus share a lot of common features. These common features are the clock, read and write signals, DMA ACK and REQ signals, interrupt line, 16 bits data bus, and 24 bits address bus. The clock is a direct line from the clock signal of the motherboard, and runs at 33.8688Mhz, as soon as the motherboard has power, regardless of the !RESET signal state. All of these signals work exactly the same as described in the ISA architecture.

The main differences are:

• 3.3v and 8v power lines
• !RESET - this line can be used as an inout, using an open collector. Setting it to ground will reset the console.
• !CS0 - unlike the ISA bus, the PSX CPU will indicate it wants to write to the PIO port using this "Chip Select" signal.
• I2S audio - this is a direct input line into the SPU. It's possible to inject an audio stream into the console's audio output through it.