The 4 x 4 and 4 x 3 multichip modules (MCM) offer a high-density packaging arrangement for the DS21Q42 T1 Enhanced Quad Framer. Either three (DS21FT42) or four (DS21FF42) silicon die of these devices is packaged in an MCM with the electrical connections as shown in Figure 1-1.
All of the functions available on the DS21Q42 are also available in the MCM packaged version. However, in order to minimize package size, some signals have been deleted or combined. These differences are detailed in Table 1-1. In the 4 x 3 (FT) version, the fourth quad framer is not populated and hence all of the signals to and from this fourth framer are absent and should be treated as No Connects (NC). Table 2-1 lists all of the signals on the MCM and it also lists the absent signals for the 4 x 3.
The availability of both a 12-channel and a 16-channel version allow the maximum framer density with the lowest cost. For example, in a T3 application, two devices (one DS21FF42 and one DS21FT42) provide 28 framers without the additional cost and power consumption of any unused framers that appear in an octal approach.