Specifications

Chapter 6 - Samples
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Shift registers
There are two types of shift registers: input and output. Input shift registers receive data in
parallel, through 8 lines and then send it serially through two lines to a microcontroller. Output
shift registers work in the opposite direction; they receive serial data and on a "latch" line
signal, they turn it into parallel data. Shift registers are generally used to expand the number of
input-output lines of a microcontroller. They are not so much in use any more though, because
most modern microcontrollers have a large number of input/output lines. However, their use with
microcontrollers such as PIC16F84 is very important.
Input shift register 74HC597
Input shift registers transform parallel data into serial data and transfer it to a microcontroller.
Their working is quite simple. There are four lines for the transfer of data: clock, latch, load and
data. Data is first read from the input pins by an internal register through a 'latch' signal. Then,
with a 'load' signal, data is transferred from the input latch register to the shift register, and from
there it is serially transferred to a microcontroller via 'data' and 'clock' lines.
An outline of the connection of the shift register 74HC597 to a micro, is shown below.
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