The DS90CR285 transmitter converts 28 bits of LVCMOS/LVTTL data into four LVDS (Low
Voltage Differential Signaling) data streams. A phase-locked transmit clock is transmitted in
parallel with the data streams over a fifth LVDS link. Every cycle of the transmit clock 28 bits of
input data are sampled and transmitted. The DS90CR286 receiver converts the LVDS data streams back
into 28 bits of LVCMOS/LVTTL data. At a transmit clock frequency of 66 MHz, 28 bits of TTL data are
transmitted at a rate of 462 Mbps per LVDS data channel. Using a 66 MHz clock, the data throughput
is 1.848 Gbit/s (231 Mbytes/s).
The multiplexing of the data lines provides a substantial cable reduction. Long distance
parallel single-ended buses typically require a ground wire per active signal (and have very
limited noise rejection capability). Thus, for a 28-bit wide data and one clock, up to 58
conductors are required. With the Channel Link chipset as few as 11 conductors (4 data pairs, 1
clock pair and a minimum of one ground) are needed. This provides a 80% reduction in required cable
width, which provides a system cost savings, reduces connector physical size and cost, and reduces
shielding requirements due to the cables' smaller form factor.
The 28 LVCMOS/LVTTL inputs can support a variety of signal combinations. For example,
seven 4-bit nibbles or three 9-bit (byte + parity) and 1 control.
