Rather than accept that it has reached the end of its life, the venerable I2C bus has regained momentum as bus repeaters extend its capabilities.
Continued interest in the decades-old serial inter-IC bus (I2C) prompted its creator, Royal Philips Electronics, to develop a family of bus repeaters that can double the number of devices able to reside on the same bus system (from 20 to 30 devices up to 40 to 60 devices). With the expanded use of the I2C as a maintenance and control bus, such as the SMBus in computing, telecommunications, and networking systems, these repeater chips will let designers build larger I2C systems than currently possible. The chips will also permit the hot-swapping of I2C cards into an active system.
Three repeater chips will initially be offered: the PCA9515, 9516, and 9518. The PCA9515 is a single repeater in an eight-lead package. It will support up to 800 pF of capacitive loading by splitting the bus into two segments. Both the 9516 and 9518 contain four repeaters, each with individual enable pins. These chips can be used like a hub, enabling the main I2C bus to send signals to four downstream I2C buses.
Available in a 16-lead package, the 9516 is limited to the four downstream ports. The 9518 comes in a larger 20-lead package. Its expansion interface allows multiple repeaters to be concatenated, so an almost unlimited number of bus segments can be added. The hub device includes bidirectional I2C drivers that isolate the bus capacitance on each segment. The hubs are multimaster-capable, which means that the repeater is transparent to bus arbitration and contention protocols. They have only one repeater delay between segments.
All three devices allow voltage translation, with either 3.3 or 5 V on any of the I2C sub-branches. The repeaters are available in both SO and space-saving TSSOP packages. The PCA9515, 9516, and 9518 cost $0.78, $1.08, and $1.20, respectively, in 10,000-unit lots. An evaluation board connects to a PC's parallel port and includes a simple to use graphical user interface. Samples and production quantities are immediately available.