What are the signals int and sas?

General information to do with the PlayStation 1 Hardware. Including modchips, pinouts, rare or obscure development equipment, etc.
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lordrafa
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What are the signals int and sas?

Post by lordrafa » May 23rd, 2021, 8:07 am

Hi,

I am being checking the service manuals for the psx and PS2 in order to try to fix my old PS2.

I have seen that no one mention the signals SAS and INT since they are not used by the DualShock.

I would like to know if there is any periferic that use them and what are they for.

Btw the SAS signal is on the central contact on top of the Gamepad conector and INT is on the eight pin inline with the others.
Thank

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Post by Shadow » May 26th, 2021, 11:36 am

Pin 8 (INT) is the interrupt line which is only used by lightguns mainly, but perhaps some special PS2 devices may use it too.

No idea what SAS is. That terminology isn't used.

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Post by lordrafa » May 26th, 2021, 9:47 pm

Shadow wrote: May 26th, 2021, 11:36 am Pin 8 (INT) is the interrupt line which is only used by lightguns mainly, but perhaps some special PS2 devices may use it too.

No idea what SAS is. That terminology isn't used.

Image
Thanks for your answer. It is interesting that gamepads doesn't use the INT signal, does this mean that the PSX/2 has too pool the dualshook to know if a button has been pressed? Do you have more info about how PSX light-gun protocol works?

On the other hand the SAS signal is connected to this PIN
Captura de pantalla de 2021-05-26 11-06-01.png
.

Pin on the side of this are GND but on the PS2 is a signal... perhaps is how the PS2 differentiate between dualshok and dualshok 2? it could be done by software too... so I am not sure...
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Post by lordrafa » May 28th, 2021, 5:18 am

Ok on the PSX that pin is "chassis ground" and SASx doesn't exist also on the official Dualshock 1 that pin is NC, hence I still think that this pin is used somehow for compatibility between PSX and PS2.

On PS2 IOP
SAS0 -> Is connected to the Dualshock port 1 and it is pulled up.
SAS1 -> Is connected to the Dualshock port 2 and it is pulled up.
SAS2 -> I assume that this was planned to be connected to PS2 Mem Card port 1, but that connection doesn't exits and are connected directly to v3.3
SAS3 -> I assume that this was planned to be connected to PS2 Mem Card port 2, but that connection doesn't exits and are connected directly to v3.3

A PS2 memcard cannot be connected to a PSX but a PSX can be connected to a PS2.

I am guessing that Dualshock 2 controllers reads that ping to detect if it is connected to a PSX (LOW) or a PS2 (HIGH) but if this is the case I am not sure is why this is routed to the IOP.

It could be that I am reading this wrong and perhaps is the PS2 the one that uses that pin to see if the controller is a Dualshock 2 or a Dualshock 1. In that case the Dualshock 2 could have that pin grounded setting SAS1/0 to LOW when connected. If a Dualshock 1 connected since that pin is NC the pull up would keep SAS1/0 to HIGH.

I assume that Dualshock 2 cannot output a HIGH value on that pin since it can be connected to a PSX where that pin is GND.

This second guest has a problem and is what happens if I connect a PSX controller with that pin routed to GND rather NC (i.e non official Dualshock or SCPH-1080?), in theory there is nothing that prevents such a device to exist.

And even more important why not to implement all this on the serial protocol?

Unfortunately I don't have any PSX/PS2 controller with me to verify this.

Anyway this looks that falls into PS2 hardware rather than PSX. I would be glad if anyone can point me in the direction of a good Ps2 community as this one is for PSX.

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Post by wisi » May 29th, 2021, 3:13 am

Code: Select all

SIO2 Registers in PS2 IOP (0x1F808200):

8270	PTSR	SIO2_REG_STAT70	Port Status Register. CDC and SAS lines states for connected device sensing.	
	3:0	r/o	CDC lines state: 0=act.low / 1=inact.high. (guess) For ports 0-3 respectively (bit 0 = port 0). 	
	7:4	r/o	SAS lines inverted state: 0=inact.high / 1=act.low. Each SAS line has a pull-up resistor. (Not tested for SAS2 and SAS3.)	
	31:8	r/o, 0.
	Bits 4 and 5 (Controller slots 1 and 2) are used by drivers (unknown exact use).


Controller port pinout:
(Looking into the Controller connector on the front of the PS2/PS1.)
Warning: Signal naming and pin numbering may differ from other documents.)
    _____________________
   |      a  bc   d      |
   | 1 2 3  4 5 6  7 8 9 |
    \___________________/



	line		default
	name		colour

1	/DSR		green	/Acknowledge
2	HLD /INT	white		/Halt(/InterruptRequest)
3	SCK		blue		Clock

4	/DTR		yellow	/Attention
5	+3.xV		red		+3.3V (+3.6V) 
6	GND		black		ground

7	+8V		gray		+7.2V..+9V Vibration motor power
8	TXD		orange	Command
9	RXD		brown		Data


a	SAS		Unknown usage. See registers descriptions.
bc	GND (shield)
d	CDC (guess) Not connected on GH-006 and all later. Unknown purpose.





The SCPH-30003 IOP has pins 184-191: CDC3, CDC2, CDC1, CDC0, SAS3, SAS2, SAS1, SAS0 - SAS0,1 go to the Memory Card and Controller buffer IC.
All CDC and SAS3,2 are connected directly to Vdd, SAS0, are connected through RB314 (resistor matrix). 



on GH-023 there is R/C gate array for expansion to SIO2

The SASn and CASn lines are inputs. On each controller port, there are three metal spring-plates over the actual pins. On their places below, they are labeled as 'a'-'d'. On the connector to the controller, there is usually a metal plate, embedded in the plastic, at least on the middle one. On the connector on the console:
    _____________________
   |      a  bc   d      |
   | o o o  o o o  o o o |
    \___________________/
(looking into the Controller connector on the front of the PS2/PS1)
'a' - Connected to SASn for the Controllers on fat consoles. There is an internal buffer on the controller & MC board. This line has pull-up resistor. It is input, most likely used for detection of some specific controller device, when pulled low. Its state should be readable from the SIO2 registers.
'b' and 'c' - Connected to GND. It is only used for shielding of the controller cable. They are two, in order to guarantee good connection. 
'd' - Connected to GND. Might have been used for detection of something at some point. Most likely would be connected to a CDCn line.
 

These inputs were not for carrying signals (most likely), but only for presence-detection of different controllers. On later models (SCPH-79000 for example) they are all (a, bc and d) grounded. 
The above is from some exploration I did on the PS2 SIO2 sometime ago.
I think they were presence-detect signals for certain, more special devices. Perhaps they would get grounded to the middle (bc) line and that would indicate something about the device connected.
It is possible that the CDC lines would also be connected on a PS2 TOOL, especially if an early model.

BTW, unrelated to the above, the SIO2 also has a differential signal mode, which is never used.

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Post by lordrafa » May 30th, 2021, 8:32 am

Hum having a differential signal is quite interesting, perharps they where thinking on faster MCs...

I have order a Dualshock 2 to do some testing, I was planing to put some tape ok BC and run GTA:VC, if my memory recalls correctly it uses the analogue feature on Dualshock 2 buttons to accelerate cars faster or slower... Obviously if you use a PSX dualshock that feature is missing, hence if this if BC is related to this the dualshock 2 with the tape would behave as the PSX dualshock....

It is a same that these details are not made public once a device comes to the end of his commercial live... it would be really interesting to know all these design decisions, why this why that, specially now that PSX/PS2 hardware is completely out of any current console.

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Post by wisi » May 30th, 2021, 9:13 am

The differential thing was I think only for controllers (because only they have common-mode chokes on the PS2 PCB) and was slower I think, though I don't remember why. I think it was meant for very long controller cables. Actually the slower thing was because the controllers have capacitors on some lines, so you can't use the 24MHz SIO2 max bit rate.

The bc point is just ground, which may also be used as shielding. It, itself is not for controller detection. That is done using commands - the PS1 and PS2 controllers identify themselves differently. See this (originally was on another website, but I can't find it): https://store.curiousinventor.com/guides/PS2/ Also PS1 controllers run SPI on 250kHz and PS2 on 500kHz I think. It was very long since I worked with them, so I may be wrong.

A lot of the protocol and everything is already known. You can see the homebrew PS2SDK IOP pad driver PADMAN code and SIO2MAN too.

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