Book Analog Interfacing to Embedded Microprocessors
erence. The Maxim MAX1242, which we have already looked at, uses an inter-
nal reference. The part can convert inputs from 0v to the reference voltage.
The reference is nominally 2.5v, but it can vary between 2.47v and 2.53v. Con-
verting a 2v input at the extremes of the reference ranges gives the following
result:
2v ¥ 1024
At Vref = 2.47v, Result = = 82910
2.47
(Note: Multiplier is 1024 because the MAX1242 is a 10-bit converter.)
So the variation in the reference voltage from part-to-part can result in an
output variation of 20 counts.
Codecs
The term “codec” has two meanings: it is short for compressor/decompres-
sor, or for coder/decoder. In general, a codec (either type) will have two-way
operation: it can turn analog signals into digital and vice-versa, or it can
annaabi.ee 
