DS80PCI800 Basic questions

Takumi Suzuki1

Mastermind 8420 points

Other Parts Discussed in Thread: DS80PCI800

Hi,

I would like to ask you some questions about DS80PCI800 as below.

Now I am planning to make following system.

TX :　 CPU =(max length 8inch)=> ”DS80PCI800” =(max length 0.4 inch)=> PCI-Slot/Card

RX：　CPU <=(max length 4inch)= ”DS80PCI800” <=(max length 8.4inch)= PCI-Slot/Card

I assume that PCIE cards are Gen2 and Gen3 certificated.

Q1) Pin-Mode

In case of using DS80PC800 as “Pin-Mode”, following settings are correct?

ENSMB	GND	Pin Mode
VDD_SEL	GND	3.3-V mode
RATE	FLOAT	AUTO Rate Select of Gen1/2 and Gen3 with de-emphasis
RXDET	FLOAT
SD_TH	FLOAT	ASSERT LEVEL is 180 mVp-p
PRSNT	1K-GND

Q2) Equalizer Setting

Q2-1) trace length

I think that the setting of EQ level will be determined by checking the real signal quality finally.

Is this correct? On the other hand, in case of “circuit design” phase, how should we set EQ?

We can set EQ according to “real trace length”, right?

Q2-2) Data sheet “Table 2”

There is a “Suggested use” column in Table 2. There describes the “Trace length”

Does this length include “internal trace length of the card which is inserted to connector” or not?

Just the length from PCIE slot pin to “ReDriver” pin, correct?

Q3) Emphasis setting

About the following note(1) of Table 3,

“The de-emphasis levels are available in GEN1, GEN2, and GEN 3 modes when RATE = Float.”

Can I understand this note that we should set “RATE” pin as “Float(Auto)” to activate the level

setting of De-Emphasis? Or the level setting will be also activated by the setting of “1K-GND(Gen1/2)”

or “1K-VDD(Gen3 with Emphasis)”?

Q4) Suggested level setting

There is a description about the trace length of RX side on “9.1.2” section.

About the sentence I underlined “Red”, my understanding is,

“We should set the level of Gen3 corresponding to Gen3 trace length under the condition of

“trace length of RX side is “< 5 Inch” and TX side is “5 inch 4-mil””.

Is this correct?

Q5）Confirmation of EQ/DEM level setting (Again)

As of now, I have understood followings.

Circuit design phase --- to set the level by the real trace length

Final (like pre-production) phase --- tuning by checking “Eye pattern”

Is this correct?

Thank you for your support.

Best Regards,

over 8 years ago

0 Takumi Suzuki1 over 8 years ago

Mastermind 8420 points

Let me post about Q4) again because the sentence I underlined (red)was lost.
The sentence is as below.

"The suggested setting for the DS80PCI800 are EQ = 0x00, VOD = 1.2 Vp-p and DEM = 0 dB." (datasheet p40, Section 9.1.2)

Thanks,
Regards,

0 Elias Villegas M. over 8 years ago in reply to Takumi Suzuki1

TI__Guru* 76130 points

Moving to high speed interface.

0 Takumi Suzuki1 over 8 years ago in reply to Elias Villegas M.

Mastermind 8420 points

Hi Elias-san,

Thank you for your kindness.

And allow me give you supplementary explanation about my questions?

Q1) Pin mode

Does ENSMB need to connect to GND via 1K ohm to set "Pin mode"?

And about PRSNT, does not need 1Kohm to connect to GND?

That is to say,

ENSMB : 1K-GND, PRSNT : Just connect to GND

Q3) EQ setting

About "RATE" setting, there is following description on the datasheet page 5.

"Tie 1K to GND = GEN 1,2" : In this setting, how do we think of "DEM" setting? DEM setting level is also active, right?

"Tied 20K to GND = GEN3 w/o De-emphasis" : In this mode, DEM setting is not active, right?

And "Tied 1K to VDD = RESERVED" : In this setting, we should not select. What is the purpose of this?

Q2) - Q5)

As i do not understand well about the relation between "Table 10 Suggested Device Setting in Pin Mode" and "Suggested use" (Table 2, 3) of EQ/DEM setting,

let me ask you these questions.

My understanding is,

About Table 10 (EQ:Level 1, DEM:Level 10), we can think this setting as "reference".

So, if our trace condition is far from the trace condition of Table 10, we can change the initail setting to another Level.

Is this correct?

Or would you reccomend us to use Table 10 as initial setting?

Thank you for your support.

0 Lee Sledjeski over 8 years ago in reply to Takumi Suzuki1

TI__Mastermind 43795 points

Hi,

Q1) Does ENSMB need to connect to GND via 1K ohm to set "Pin mode"?

A1) ENSMB must be pulled to GND for pin mode operation. A 1K resistor is recommended, but this pin can be tied directly to GND if there is no space for the resistor.

Q1a) About PRSNT, does not need 1Kohm to connect to GND?

A1a) The PRSNT pin has the same answer. A 1K resistor to GND is recommended for normal operation, but this pin can be tied directly to GND as well.

Q2) Equalizer setting

A2) In PCIe it is very common for the CPU and PCIe Cards to use Tx Preset 7. This setting has a large amount of boost, so the best DS80PCI800 setting is usually much lower than the datasheet suggestions. I would start with an EQ setting of "Level 1". EQx1=0 EQx0=0

Q3) De-emphasis setting

A3) Setting the RATE pin to "Float" is recommended. An internal rate detection circuit will sense GEN2 or GEN3 automatically. Usually a DEM setting with 0 dB or - 3.5dB will work best in PCIe applications. I would start with Level 4 or Level 10. PCIe CPU and Cards have built in CTLE circuitry to help compensate for some of the trace attenuation.

Q4) Suggested level setting

A4) I would use the Table 10 suggestions first. It is easier to tune the system by adding additional equalization and arrive to an optimum result.

Q5) Confirmation of EQ/DEM level

A5) Yes the final tuning is usually based on internal eye margin.

Regards,

Lee

0 Takumi Suzuki1 over 8 years ago in reply to Lee Sledjeski

Mastermind 8420 points

Hi Lee-san,

Thank you very much for your kind reply.
I understood well.

But let me confirm one thing as below about RATE setting.

RATE : "Tie 1K to GND = GEN 1,2"

In this setting, Can I understand that DEM setting level is also active?

Thanks in advance, Regards,

0 Lee Sledjeski over 8 years ago in reply to Takumi Suzuki1

TI__Mastermind 43795 points

Hi Takumi-san,

Yes, the DEM setting is active when RATE pin is set to GND with 1K resistor.

Regards,

Lee

0 Takumi Suzuki1 over 8 years ago in reply to Lee Sledjeski

Mastermind 8420 points

Hi Lee-san,

Thank you for your answer!

I understood.

Regards,

Interface

Interface forum

DS80PCI800 Basic questions