The DS90CR215 transmitter converts 21 bits of CMOS/TTL data into three LVDS (Low Voltage
Differential Signaling) data streams. A phase-locked transmit clock is transmitted in parallel with
the data streams over a fourth LVDS link. Every cycle of the transmit clock 21 bits of input data
are sampled and transmitted. The DS90CR216 receiver converts the LVDS data streams back into 21
bits of CMOS/TTL data. At a transmit clock frequency of 66 MHz, 21 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 1.386
Gbit/s (173 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 21-bit wide data and one clock, up to 44
conductors are required. With the Channel Link chipset as few as 9 conductors (3 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 21 CMOS/TTL inputs can support a variety of signal combinations. For example, five
4-bit nibbles plus 1 control, or two 9-bit (byte + parity) and 3 control.
