Dallas Semiconductor introduced the DS21600 series of clock rate adapters, integrated circuits for converting signal frequencies between E- and T-carrier clock rates without external components. The devices are designed to be completely pin and software compatible with Level One's recently discontinued LXP600ASE, LXP602SE, LXP604SE and LXP610SE CLock ADapter (CLAD) products, enabling designers to easily continue working with applications that combine T1 or E1 rates.

Different frequencies are used for data transmission in different enterprise networks around the world. T1 in North America transmits at a rate of 1.544 Mbps, while E1, the European protocol, transmits at the rate of 2.048 Mbps. The two data rates converge in several kinds of access equipment, including Add/Drop Multiplexers (ADMs), DSL Access Multiplexers (DSLAMs), Channel Service Units (CSUs), channel banks, routers, switches and other related equipment.

A CLAD chip receives a T1 or E1 frequency and outputs it along with a higher multiple rate. The chip keeps the output phase locked to the input clock to minimize jitter and avoid data loss. The conversion function is also used in applications that multiplex data coming off the T1/E1 streams onto a single backplane. Dallas is providing several parts, including the DS21600 and DS21602 that perform data conversions between 1.544 MHz and 2.048 MHz, the DS21604 that converts between 1.544 MHz and 4.096 MHz and the DS21610 that produces multiple frequencies up to 8.192 MHz.

These are highly opportunistic parts -- and I love that! Letting another company forage around in a market, creating a need and a decent pricing structure, then abandoning it must have looked like a gift horse to Dallas Semiconductor; especially as the product know-how was already in house. These are quite simple parts with an analog PLL and feedback driven by the clock of one standard (E, or T) producing two locked clock outputs in the other standard, one of which can be a higher multiple. A third output produces an 8 kHz clock which is locked to the clock input and, if present, a sync input. No external components are required and operation is from a single 5-V supply.

Apart from providing pin-for-pin replacements for the LXP600ASE, LXP602SE and the LXP604SE in 16-pin SOIC, Dallas will also be manufacturing the parts in DIP-8 which I see as much more sensible. People are often surprised at how many multi-standard parts are required, but even in the continental U.S. there are many thousands of E- circuits mixed in with T- circuits; there are many switches and interfaces between standards particularly along the seaboard states and in dedicated circuits to international companies.