Sequential logic systems
J. R. Gibson · 2013
Large logic networks may be constructed as assemblies of readily available integrated circuits; the exceptionally high reliability of these devices ensures that networks containing large numbers of SSI, MSI and LSI devices will function correctly. Often the cost of assembling a network forms a significant part of the total manufacturing cost (including purchase of the integrated circuits), so that the use of a small number of LSI devices instead of a large number of SSI and MSI devices may reduce total costs. Also a reduction in the number of components usually increases the, already high, system reliability. Consequently designers try to minimize the number of integrated circuits required in large networks by using large scale devices. However, as most new network designs implement functions for which LSI devices are not available, the use of a small number of devices may require the manufacture of a unique LSI device for a user’s special requirement. Such an integrated circuit is an Application Specific Integrated Circuit (ASIC) . Although integrated circuit manufacturing costs are low when many identical devices are made, the cost of preparing a new design is extremely high. Therefore, unless production quantities will be high, designers of large logic networks sometimes have to choose between low assembly costs using expensive ASICs and high assembly costs using available SSI and MSI devices.