SCEA117 July 2022 SN74HCS164 , SN74HCS164-Q1 , SN74HCS165 , SN74HCS165-Q1 , SN74HCS595 , SN74HCS595-Q1
Any shift register can be daisy-chained, so long as it has a serial data input and direct access to the last serial register’s contents. In order to connect two shift registers in series, connect the serial output of one device (usually QH or QH’) to the serial input (usually SER) of the next device. Typically, all of the clock signals will be shorted together, although they can be separated for unique cases.
Figure 1-4 provides an example of connecting two 595 function shift registers together to convert 3 output pins into 16 output pins (O0 to O15). The first device connects to the system controller as usual, with the serial data and clocks coming directly from the controller. For the second device in the chain, the only difference is that the data input comes from the QH’ output of the previous device rather than the controller.
Figure 1-5 shows an example of connecting two parallel-in and two parallel-out shift registers to provide 16 new inputs and 16 new outputs. By using this configuration, the number of I/Os required by the controller remains only four, while the number of outputs (or inputs) can be increased almost indefinitely. There are multiple design challenges that need to be addressed to ensure proper operation. See Section 2 for details.