Bi-directional scan flip-flop circuit and method

A circuit series comprising:

• first and second input/output (I/O) nodes;
• and
• a plurality of scan flip-flop circuits arranged as first through last scan flip-flop circuits coupled in series,
• wherein
• the first scan flip-flop circuit comprises a selection circuit coupled to the first I/O node and configured to receive a scan direction signal,
• the last scan flip-flop circuit comprises:
• a flip-flop circuit comprising an output terminal;
• a first driver configured to receive the scan direction signal and a scan enable signal, the first driver comprising:
• an input terminal coupled to the output terminal of the flip-flop circuit;
• and
• an output terminal coupled to the second I/O node;
• and
• a second driver configured to receive the scan direction and scan enable signals, the second driver comprising an input terminal coupled to the output terminal of the flip-flop circuit, and
• responsive to the scan direction and scan enable signals, one of:
• the first driver is configured to output a first signal responsive to a second signal received at the first I/O node, or
• the second driver is configured to output a third signal responsive to a fourth signal received at the second I/O node.

A method of operating a scan flip-flop circuit, the method comprising:

• outputting a first signal from a selection circuit to a flip-flop circuit;
• in response to the first signal, outputting a second signal from the flip-flop circuit;
• receiving a scan direction signal and a scan enable signal at each of the selection circuit and first and second drivers;
• in response to the scan direction and the scan enable signals, either
• outputting the first signal in response to a third signal received at the selection circuit and outputting a fourth signal from the first driver in response to the second signal, or
• outputting the first signal in response to a fifth signal received at the selection circuit and outputting a sixth signal from the second driver in response to the second signal.