Multiple driver resolution

The wor nets and wand nets are used when multiple driver resolution needs to be performed using or-logic and and-logic respectively. Upon synthesis, multiple drivers of such a net are connected together by an or gate (for a wor net) and by an and gate (for a wand net). Here is an example that shows this effect. 

When there are multiple drivers on a net, a resolution function is needed to resolve the final value on the net. In VHDL, one can create resolution functions and associate it with a datatype or a signal object. std ulogic is an example of an unresolved datatype, while stdjogic is an example of a resolved datatype. The resolution function is used to figure out the final value on a signal when there are more than one driver on it. In Verilog, one can t have user defined resolution functions. Instead one can use net types with built in resolution functions (pre-defined in Verilog) such as wand, wor, and so on. 

Many fluorescent dyes and proteins now available enable multiple detection channels and the ability to multiplex related assays. HCS assays typically use at least two channels one for a DNA stain and another for the fluorophore of interest. In general, the maximum number of channels utilized at one time ranges from two to five. Instrument hardware and driver software determine the number of channels and fluorophores to be acquired. Some factors to consider here include illumination source (arc lamp or laser), filter and mirror requirements, number of cameras or PMT detectors, camera sensitivity, and desired detection wavelength range. Other considerations for multiplexing include read time, resolution, and assay time (for live cell imaging). 

Two key issues in SECM are speed and resolution. These are tied to the nature of the available tips and the techniques used to move them in the vicinity of the sample. One approach to greater speed is the use of multiple tips. There are a number of approaches to the fabrication of an array of tips. A problem with these arrays is alignment of the array with the sample so that all of the tips are at the same or a known distance from the sample. This can be accomplished by having each tip on its own controllable positioning device, such as an array of cantilevers with individual piezoelectric control (32,33). For example, 50 cantilevers with a 200-/xm period (to cover a span of 1 cm) were fabricated with integrated piezo sensors and zinc oxide actuators. Such an array provided 35 A resolution and a 20 kHz bandwidth. A difficulty with such arrays is the complexity of the instrumentation needed to use them. Each sensor in the array essentially needs its own driver and potentiostat. An alternative would be an array of individually addressable tips on a single chip that all move in the x, y, and z directions in unison. This would require some additional means to orient and align the array chip... 

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