Picture end token in a system comprising a plurality of pipeline stages

In a system having an input, an output and a plurality of processing stages between the input and the output, the improvement characterized by:

• an interactive metamorphic interfacing token, defining a universal adaptation unit for control and/or data functions among said processing stages, said token being transmitted from one of said processing stages to an immediately succeeding processing stage along a data flow path, and said token incorporating an extension bit, wherein sequential processing stages are connected by two-wire interfaces, and further comprising:
• electrical validation circuitry in at least one processing stage to generate a validation signal for a first state when data stored in said stage is valid and for a second state when data stored in said stage is invalid, said state defining said stage's ability to accept data, said validation circuitry including at least one validation storage device to store said validation signal for the corresponding pipeline stage;
• an acceptance signal connecting an adjacent pair of processing stages and conveying an acceptance signal indicative of the ability of said successive pipeline stage to load data stored in the preceding pipeline stage;
• and
• enabling circuitry connected to said data storage devices for generating an enabling signal to enable loading of data and validation signals into the respective storage devices,
• wherein:
• said data storage devices include a primary data storage device and a secondary data storage device;
• said data is loaded into said respective primary data storage devices and said validation signal is loaded into a respective primary validation storage device at the same time;
• data is loaded into said respective primary data storage device when said acceptance signal assumes an enabling state;
• and
• said acceptance signal assumes said enabling state only when the acceptance signal associated with the data storage device of said next successive pipeline stage is in said enabling state or said data in said data storage device of said next successive pipeline stage is invalid;
• wherein said token is a PICTURE.sub.-- END token for indicating the end of an individual picture.