Key learnings:
- Buffer Register Definition: A buffer register is defined as a storage unit for binary words, constructed using flip-flops to store each bit.
- Data Loading: Data is loaded into a buffer register at each clock tick, with outputs matching input bits at each leading clock edge.
- Uncontrolled Outputs: Buffer registers do not control inputs, leading to uncontrolled outputs.
- Controlled Buffer Register: A controlled buffer register uses tri-state switches to control data loading and retrieval.
- Operation Control: In controlled buffer registers, control lines manage when data is stored or read from the register.
A buffer register stores a binary word. Each bit sits in one flip-flop, so an n-bit word needs n flip-flops. A 4-bit synchronous example uses four D flip-flops. The word B1B2B3B4 loads on one clock edge. After that rising edge the outputs equal the inputs: Q1 = B1, Q2 = B2, Q3 = B3 and Q4 = B4.
Buffer registers of that simple kind have no enable on the data path, so the outputs follow every clocked load. A controlled buffer register adds that enable.
Tri-state switches gate load and read. Pull the 
or 
control line (blue) low to store a word. Pull the 
control line (red) low to read it.
