Analog Interfacing to Embedded Microprocessor Systems, 2nd Edition

is changed, the system has to be recalibrated. The PROM has to be as big as the

number of CCD pixels times the ADC resolution. A 1024-element CCD followed

by an 8-bit ADC would require a PROM 256  1024  8 bits wide. The timing

logic has to be sure that the low address (pixel number) corresponds to the

correct high address (converted pixel output).

A PROM was used in Figure 3.23 to illustrate the principle; in practice you

would normally want this table to be stored in RAM or flash memory so the

microprocessor could modify it. You can implement the same normalization

technique in software if the microprocessor can keep up with the data rate. The

microprocessor has to have a lookup table the same size as the PROM. For each

sample, the pixel value