Scan Chain Length Calculator
Work out scan chain length instantly with clear inputs, formula shown and shareable results.
About Scan Chain Length Calculator
Scan test time is patterns times chain length divided by the scan clock, so doubling the number of chains halves test time. The limit is the number of available scan pins, which is why on-chip compression is used to drive hundreds of internal chains from a handful of pins.
Formula
Scan test time
chain length = flops / chains; test time = patterns x (chain length + 1) / scan clock
Worked example
With the default values below, Scan Chain Length Calculator returns Flops per chain of 3,750. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Scan flip-flops
- 240,000 flops
- Scan chains
- 64 chains
- Test patterns
- 8,000 patterns
- Scan clock
- 50 MHz
Results
- Flops per chain
- 3,750 flops
- Test time
- 0.60 s
- Total shift cycles
- 30,008,000 cycles
- Test data volume
- 3,840.00 Mbit
Step by step
- 1Values used
- 2Scan test time
- 3Flops per chain= 3,750 flops
- 4Test time= 0.60 s
- 5Total shift cycles= 30,008,000 cycles
- 6Test data volume= 3,840.00 Mbit
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is test time so expensive?
Automated test equipment time is charged per second and ATE is capital intensive. Test time often exceeds a second per die and directly adds to unit cost.
What does scan compression do?
It decompresses a small input stream into many internal chains and compacts responses on the way out, cutting both data volume and time by 10-100 times.
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