Hybrid scan chains with flip-flops and latches

A method to interface between a last flip-flop in a flip-flop-based part of a scan chain with a first latch in a latch-based part of the scan chain, wherein the latch-based scan chain comprises a chain of scannable latches, the method comprising:

• in an interface memory element, storing a value of the last flip-flop in the flip-flop-based part of the scan chain to obtain a stored value before or at a time of asserting clock inputs of flip-flops in the flip-flop-based part of the scan chain;
• and
• after the time of asserting the clock inputs of the flip-flops in the flip-flop-based part of the scan chain, using the stored value to set the value of the first latch in the latch-based part of the scan chain.

A method to interface between a last flip-flop in a flip-flop-based part of a scan chain with a first latch in a latch-based part of the scan chain, wherein the latch-based scan chain comprises a chain of scannable latches and the first latch in the latch-based part of the scan chain is not data carrying in a functional mode, the method comprising:

• before a time of first asserting a clock input of the last flip-flop in the flip-flop-based part of the scan chain, deasserting a flush input or a scan control input of the first latch in the latch-based part of the scan chain to store a value of the last flip-flop in the flip-flop-based part of the scan chain;
• and
• before a time of second asserting the clock input of the last flip-flop in the flip-flop-based part of the scan chain, asserting and de-asserting flush inputs or scan control inputs of latches in the latch-based part of the scan chain using non-overlapping pulses to assert and de-assert the flush inputs or to assert and de-assert the scan control inputs.