PTN3460 with 4-lane source

[jseo91]

Hello,

I would like to use PTN3460 for my product, but my DP source has 4-lane. 

The higher resolution or faster rate is not an issue, but I just want to make sure 4-lane source is backward compatible with PTN3460 (2-lane converter). 

I did a bit of research and there is a DPCD register that controls the number of lanes(MAX_LANE_COUNT ),

so I don't think it should be a problem, but would you be able to confirm that it should work?

Thank you in advance! 

[jseo91]

Hello Jozef,

My DP source does have 4 lanes. 

Although PTN3460 has only 2 lane connection, I was hoping that DP source will detect that the sink device can handle only 2-lane, and stream with 2-lane option.

The following is from Displayport specification document:

2.1.1 Number of Lanes and Per-lane Data Rate (Applicable both in SST and MST Modes)
DisplayPort supports three options for the number of Main Link lanes and two options for Main Link data rate
per lane as follows:
• 4-, 2-, or 1-lane
• 5.4Gbps, 2.7Gbps or 1.62Gbps per lane
The link layer specification and data mapping specification in particular, is defined to facilitate the support of
these lane count options.
The per lane data rate is determined not only by the capabilities of DisplayPort transmitter and receiver but
also by the quality of a channel, or a cable.
The DisplayPort Sink device must indicate the capability of its receiver in the receiver capability field of the
DPCD, as described.
After reading the receiver capability, the DisplayPort Source device must configure the link by writing to the
link configuration field of the DPCD in the DisplayPort Sink device and then running link training.
Through this process of receiver capability discovery and link training, the DisplayPort Source and Sink
devices are able to negotiate for the optimal lane count and per lane data rate for a given connection.

According to the docuement, if I understood right, the DP source would change its stream configuration and stream with 2-lane option. 

So my theory was the DP source will communicate with PTN3460 and read the registry which says MAX_LANE_COUNT is 2, and the DP source will stream with 2-lane option. 

It's not like I want it to stream with 4 lanes. I just want to make sure DP source can stream with 2 lanes after communicating with PTN3460 while it has 4 lane connections (lane2 and lane3 will be left floating).

Am I missing something here? 

Thank you in advance.  

[JozefKozon]

Hello JH SEO,

the PTN3460 will work with the two lanes, if the other two lanes will be floating. So we can guarantee, that the PTN3460 will converse the two DP stream to LVDS protocol if it will be set to DP 2-lane mode in the MAX_LANE_COUNT. The MAX_LANE_COUNT must be 2. 

But how will the displayport (DP source) react to the two floating lanes, I don't know. The DP source is not our product, so we cannot guarantee under which conditions it will work. 

With Best Regards,

Jozef

[JozefKozon]

Hello JH SEO,

please refer to the section 8.1.1 in the PTN3460 datasheet. The PTN3460 is capable to operating in maximum 2-lane mode. It cannot work with 4-lane. You can decrease the number of lanes in the MAX_LANE_COUNT to one, but it cannot be increased to four.

I apologize for inconvenience.

With Best Regards,

Jozef

[jseo91]

Wouldnt the source change its setting to 2 lane to stream its display after communicating to PTN3460? 

I dont wish to have high resolution and fast rate; I only need 1920 1080 60hz spec. 

Thank you in advance

[JozefKozon]

Hello JH SEO,

I am not sure about your configuration. However please refer to the Figure 2. in the PTN3460 datasheet. The PTN3460 has physically only two DP lanes to the DP source, so there can be only 2 DP lanes connected. 4 DP lanes cannot be connected to the PTN3460.

I apologize for inconvenience.

With Best Regards,

Jozef

[jseo91]

Please refer to my another question posted above; I accidentally didn't reply directly under your answer. Thank you in advance!