Legacy Upgrades Call For 3U CompactPCI
Electronic sub-systems for military applications have traditionally been custom designed to meet the precise size and performance requirements of the application at hand. Custom designs, however, are becoming impractical and inefficient as military applications become faster, more powerful and more cost-effective than ever before.
As applications are requiring smaller sub-systems with more processor power and more flexibility, 6U VME or SEM-E modules are being phased out. System designers are increasingly turning to the smaller but more flexible 3U CompactPCI for their COTS solutions.
3U VME Falls Short
Although 3U VME is not necessarily inappropriate or obsolete for military applications, it is losing the race against CompactPCI (cPCI). The advantage of the J2 connector for cPCI is the ability to provide backplane I/O, which 3U VME cannot accommodate. For applications involving high shock and vibration, the advantage is decisive. The limited bus bandwidth and the lack of rear I/O pins on 3U VME poses a problem. There is no way of connecting I/O signals to the backplane. With 3U VME, the only possibility for realizing I/O connections is via the front side. However, in the case of conduction-cooled boards, the front panel space is very limited. This makes providing front panel I/O difficult. The situation is completely different with 32-bit 3U cPCI. Depending on the slot (system or peripheral) in which the board is inserted, a 32-bit cPCI bus system provides 75 rear I/O pins for the system slot and 105 for each peripheral slot (Table 1). Thus, a fully extended system with 8 slots provides a maximum of 810 I/O pins across the backplane. If replacement is necessary, the module can be removed immediately and replaced by a new one. This way, detaching the front connectors is avoided.