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 is coupled to the second I/O node and comprises first and second drivers configured to receive the scan direction signal and a scan enable signal,
• responsive to the scan direction signal having a first logic level,
• the selection circuit is configured to output a flip-flop input signal responsive to a first signal received at the first I/O node, and
• the first driver is configured to, further responsive to the scan enable signal having a second logic level, output a second signal to the second I/O node responsive to the flip-flop input signal, and
• responsive to the scan direction signal having the second logic level,
• the second driver is configured to, further responsive to the scan enable signal having the second logic level, output a third signal responsive to a fourth signal received at the second I/O node, and
• the selection circuit is configured to output the flip-flop input signal responsive to the fourth signal.

A method of performing a scan operation, the method comprising:

• receiving a scan direction signal and a scan enable signal at each of a selection circuit, a first driver, and a second driver of a scan flip-flop circuit;
• in response to the scan direction signal having a first logic level and the scan enable signal having a second logic level, using the selection circuit and the first driver of the scan flip-flop circuit to propagate a first data bit in a forward scan direction;
• and
• in response to the scan direction signal having a second logic level, using the selection circuit and the second driver of the scan flip-flop circuit to propagate a second data bit in a reverse scan direction.