IDT ASIC demuxes to multiple displays from one DisplayPort signal

One of the big differences between DisplayPort and other display interfaces, such as HDMI or DVI, is that the latter transmit video data as continuous bit streams, while DisplayPort transmits the data in packets and allows for asymmetric two-way transfers. If your application is simply connecting a graphics chip to a display, packetizing creates a lot of overhead for little real benefit. But if you are driving multiple displays, there are some advantages to all that extra work.

Now personally, I can’t imagine wanting multiple displays. But if you are an investment or commodities trader, for instance, you need as many displays as possible to show your boss that you are working hard enough to justify your seven-digit bonus. More realistically, if you are a chip designer or mechanical engineer who has to multitask as a matter of routine, you actually do need multiple displays just to make up for the lameness of Microsoft’s window manager. Ji Park, vice president and general manager of the display and video group at IDT, said that in his own small-sample personal survey, about 30 percent of engineers in Japan and 50 percent in Korea had more than one display running at once.

Both operating-systems developers and the graphics folks have made provision for this. Park claims that many computers, including some notebooks, can support a viewing space much wider than a single screen. So the data is there to drive multiple displays. The question is how to get the data to the right display.

One approach, according to Park, has been to use an additional display-driver card per monitor in the computer chassis. Another is with an external splitter box. Both of these approaches, Park said, can cost hundreds of dollars and consume 100W or so. Another alternative is to go to USB display links, but that quickly runs into bandwidth problems. And the poor folks in Hollywood who scrape by selling movies are very touchy about unencrypted video going over USB, even if most of it isn’t theirs.

IDT thinks it may have a better idea, with the VMM 1300 PanelPort ViewXpand chip. This device, powered by the DisplayPort cable at less than 1.5W, is basically a router for DisplayPort micropackets. The chip inspects incoming micropackets, sorts them out based on the pixel addresses, modifies the address to correspond to the screen coordinates on the appropriate monitor, and routes each packet to said appropriate monitor. The chip is designed to work in either of two modes: acting as a hub in a dongle, in which case it can route packets to any of three output ports; or in a daisy-chain topology, in which case you only use two outputs, and you can string out as many chips and monitors as your graphics bandwidth allows.

The chip can also function as a protocol converter, so in hub mode you can drive legacy display interfaces on the chip outputs. Since the chip works by routing the existing DisplayPort packets, it requires no new driver software and is entirely compatible with the collection of DisplayPort standards, including HDCP v1.3 content protection. That is a big deal if one of your monitors will be handling content-protected video.

The design also takes advantage of the bidirectional abilities of DisplayPort. At initialization the chip uses identification cycles to figure out what monitors it will be driving and to map the viewing window onto the various monitors screen coordinates, thereby setting up the routing table.

Park said the IDT VMM 1300 is sampling now, with production chips available in August.