Clock domain crossing
Encyclopedia
A clock domain crossing or simply clock crossing, is when a signal crosses from one clock domain into another. If a signal does not assert long enough and is not registered, it may appear asynchronous
on the incoming clock boundary.
Synchronizing a signal that crosses into a higher clocked domain can be accomplished by registering the signal through a flip-flop
that is clocked by the source domain, thus holding the signal long enough to be detected by the higher clocked destination domain. Synchronizing a signal traversing into a slower clock domain is more cumbersome. This typically requires a register in each clock domain with a form of feedback from the destination domain to the source domain, indicating that the signal was detected.
Asynchronous communication
In telecommunications, asynchronous communication is transmission of data without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data from the communication symbols is encoded within the symbols...
on the incoming clock boundary.
Synchronizing a signal that crosses into a higher clocked domain can be accomplished by registering the signal through a flip-flop
Flip-flop
Flip-flops, thongs, Japanese sandals, or jandals are an open type of outdoor footwear, consisting of a flat sole held loosely on the foot by a Y-shaped strap, like a thin thong, that passes between the first and second toes and around either side of the foot...
that is clocked by the source domain, thus holding the signal long enough to be detected by the higher clocked destination domain. Synchronizing a signal traversing into a slower clock domain is more cumbersome. This typically requires a register in each clock domain with a form of feedback from the destination domain to the source domain, indicating that the signal was detected.
See also
- Crosstalk (electronics)Crosstalk (electronics)In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel...
- Metastability in electronicsMetastability in electronicsMetastability in electronics is the ability of a digital electronic system to persist for an unbounded time in an unstable equilibrium or metastable state....
- globally asynchronous locally synchronousGlobally asynchronous locally synchronousGlobally asynchronous locally synchronous is a circuit that consists of a set of locally synchronous modules communicating with each other via asynchronous wrappers. Advantages include lower power consumption and electromagnetic interference...
- The topic is duplicated in Flip-flop (electronics)#Timing considerations