SPI Bus Timing Calculator
Bit period, frame time and throughput for an SPI bus.
Input
ℹ SPI moves 1 bit per SCK edge, so throughput = SCK.
Find Component lists logic level shifters for cross-voltage SPI (e.g. 3.3 V ↔ 1.8/5 V) — pick one rated above your SCK rate.
Find Component lists logic level shifters for cross-voltage SPI (e.g. 3.3 V ↔ 1.8/5 V) — pick one rated above your SCK rate.
Results
Bit Period—
Frame Time—
Throughput—
💡 Usage & Formula
bit period = 1/SCK, frame time = bits/SCK, throughput = SCK (1 bit per clock).
When you need it: Confirming an SCK frequency the slave can accept, and checking that setup/hold plus trace flight-time still leave a valid sampling window at high clock rates.
Worked example: SCK = 10 MHz → bit period 100 ns; a 24-bit frame takes 24 × 100 ns = 2.4 µs and throughput is 10 Mbit/s (one bit per clock). Push to 50 MHz over 15 cm of FR-4 (~1 ns each way) and the round-trip flight time starts eating the read window.
Tips & gotchas:
- At high SCK the slave's output-valid time plus trace delay can force a lower clock or a delayed sampling phase.
- CPOL/CPHA (SPI mode) must match on both ends, or every byte is shifted/inverted.
- Add series (source) termination on SCK for long traces to tame ringing and overshoot.
- Respect CS-to-first-clock setup and last-clock-to-CS hold; many slaves latch on the CS edge.
📖 References:SPI (Wikipedia)