DS21FT42

The Four x Four and Four x Three MCMs offer a high density packaging arrangement forthe DS21Q42 T1 Enhanced Quad Framer. Either three (DS21FT42) or four (DS21FF42)silicon die of these devices is packaged in a Multi-Chip Module (MCM) with the electricalconnections as shown in Figure 1-1.

All of the functions available on the DS21Q42 are also available in the MCM packagedversion. However, in order to minimize package size, some signals have been deleted orcombined. These differences are detailed in Table 1-1. In the Four x Three (FT) version,

the fourth quad framer is not populated and hence all of the signals to and from this fourthframer are absent and should be treated as No Connects (NC). Table 2-1 lists all of thesignals on the MCM and it also lists the absent signals for the Four x Three.

The availability of both a twelve and a sixteen channel version allow the maximum framerdensity with the lowest cost. For example, in a T3 application, two devices (oneDS21FF42 and one DS21FT42) provide a total of 28 framers without the additional costand power consumption of any unused framers that appear in an octal approach.