DisplayPort 1.2 MST and STMicro Athena Controller
Ah, DisplayPort MST – this mythical technology that has been buzzing in my head since AMD first started talking about multi-display gaming many moons ago. It is no coincidence that the first thing that shows up when you Google "DisplayPort MST" is a post about Eyefinity and MST capable devices and that I got so excited when I saw a MST hub at CES this past January. DisplayPort 1.2, apporoved in December of 2009, officially added support for higher bandwidth connectivity and multiple streams for daisy chaining. Since then it has been a wait for devices to actually utilize it.
The platform used on the ASUS PQ321Q is a unique implementation of exactly this.
The ASUS PQ321Q (and the Sharp PN-K321) are both powered by STMicroelectronics Athena controller billed as "a series of innovative System-on-Chip (SoC) controllers designed for multifunctional monitors with a maximum resolution of up to 2560 x 1600 (STDP93x0), 1920 x 1200 (STDP73x0), and 120 Hz FHD (STDP9210)." Even though it says we are dealing with a max resolution of 2560×1600, there is a lot of headroom on these controllers and when paired up in a multi-head evironment we are able to run parallel 1920×2160 @ 60 Hz screens on a single LCD.
STMicro "Athena" SoC used in the ASUS PQ321Q
These ICs from STMicro combine DP 1.2 transmitters and receivers in addition to HDMI 1.4 receivers and can support 3D video sources as well. They can capture up to 4096×2160 resolution video and can scale that down to just about any resolution or it can be passed through to an LVDS connection unchanged. In the configuration on the monitors in question though they are configured to drive a multi-stream display.
Though I didn't take the PQ321Q apart, I have seen a development board from STMicro and the logic and processing on the system is not insubstantial, with a couple of downscalar boards and quad LVDS connections to the panel itself. Each display head is responsible for half the screen – up to 1920×2160 at 60 Hz.
Because of the odd configuration, I have seen some comments from readers calling what ASUS, Sharp and STMicro are doing a "hack" to get 4K working at 60 Hz refresh rates. While you could label it that way I consider it an innovative use of current technologies – by utilizing the multi-stream technology in a single panel we are able to basically push twice the amount of pixels per second than you would otherwise get in a monitor like this. And the truth is that while DisplayPort 1.2 has the bandwidth to support 4K resolutions at 60 Hz with a single stream, the necessary controllers for that option are not yet available. Because timing controllers needed for that much bandwidth aren't going to ship at all until early to mid 2014 (likely in small quantities) you can expect the tiled display option to be around for some time to come and remain the budget 60 Hz 4K option as well.
This doesn't come without some complications of setup as we'll see on the next page of our story here, but I really think that pushing the envelope like this to release higher density panels at consumer cost levels is what the PC industry needs to innovate.