SIPO: Why N Cycles Are Required Before First Valid Output
Communication protocols like SPI and UART rely on shift registers to convert incoming serial bitstreams into parallel data bytes.
The circuit features a 4-bit Serial-In Parallel-Out (SIPO) shift register. The serial data input is DIN and the parallel output is Q[3:0]. Incoming data enters at Q[3] and shifts right toward Q[0] on each clock cycle. The register initializes to 0000 at reset. A serial bitstream of 1, 1, 0, 1 arrives on DIN sequentially over four clock cycles to form a final parallel word.
Trace the state of Q[3:0] over the four clock cycles. Determine the exact cycle when the parallel output contains a complete, valid data frame and identify the architectural requirement for safely reading this data.
Constraints
- The shift register shifts data on the rising edge of the clock.
- Data at
DINis stable before the clock edge. - The initial state of
Q[3:0]is strictly0000.
Topics
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