Page 136 - Handout Digital Electronics

Serial Load Register

In serial load, the output of each flip flop is connected to the input of the next flip-flop. For a D flip-
flop, the data on the D input is transferred to the output when a clock pulse is applied.

Figure 65: Serial load register

Example of load operation

Assume that a data word to be loaded serially in the register is 1101. In serial load, the most significant
bit is to be loaded first. If a 1 is applied to the input of the first flip-flop (FF0) and a clock pulse applied
that data will be entered and stored in flip-flop FF0. In the next clock pulse, the next binary 1 will be
applied at the D input. The 1 in the first flip flop (FF0) will be shifted to FF1 and in the next clock pulse
a 0 will be applied to FF0. FF0 will now store a 0, FF1 a 1 and FF2 a 1. In the last clock pulse FF0 will
store a 1, FF1, a 0, FF2 a, 1 and FF3 a 1. To load 4 bits serially in a register four clock pulses are
needed. The example below shows the serial load operation.

FF0 FF1 FF2 FF3

Initially 0 0 0 0

Pulse 1 1 0 0 0

Pulse 2 0 1 0 0

Pulse 3 1 0 1 0

Pulse 4 0 1 0 1

Activity

1) Given the bit stream 101, show that performing binary multiplication and binary division
are
equivalent to:

(i) Shift one bit at a time to he left

(ii) Shifting one bit at a time to the right

2) Show that serial data entry is equivalent to shifting 1-bit to the right at a time

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