Block Write

Block Write

Block Write is an EPC Gen2 command that writes multiple 16-bit memory words to an RFID tag in a single transaction. Standard Gen2 Write commands operate on one word at a time, with each word requiring a separate command-response cycle. Block Write dramatically improves encoding throughput by batching multiple words into a single RF exchange, making it essential for high-speed commissioning and source tagging operations.

Performance Comparison

A standard word-by-word write to a 96-bit EPC requires six individual Write commands (96 bits / 16 bits per word = 6 words). Each Write command involves a reader-to-tag command, tag processing time, and tag-to-reader acknowledgement — roughly 20 ms per word, totalling approximately 120 ms for a full EPC encode.

Block Write can transfer the same six words in a single command-response sequence, reducing total encode time to approximately 40-60 ms depending on the tag IC and RF conditions. For User Memory writes involving dozens of words, the speed improvement is even more significant.

How It Works

The reader issues a BlockWrite command specifying:

• Memory bank: Target bank (01 for EPC Memory, 11 for User Memory)
• Word pointer: Starting word address
• Word count: Number of 16-bit words to write
• Data: The concatenated word values

The tag receives the entire data payload, writes all words to its EEPROM, and returns a single acknowledgement. If any word fails to programme correctly, the tag returns an error and the reader must retry. Some ICs support partial-success reporting, indicating which words were successfully written.

Tag IC Support

Not all tag ICs support Block Write. Support depends on the chip manufacturer and model:

• Impinj Monza series: Supported (up to EPC bank)
• NXP UCODE series: Supported with configurable block sizes
• Impinj M700 / M800: Supported

When designing a commissioning system, verify Block Write support against the target IC's datasheet. If Block Write is unavailable, the system must fall back to sequential word writes with proportionally longer encode times.

Use in Production Lines

In source tagging facilities, conveyor speeds and line throughput depend directly on tag encoding time. A production line running at 60 items per minute has one second per item for all operations — printing, encoding, and verification. Block Write's ability to encode a full EPC in under 60 ms leaves ample margin for print and verify steps.

For tags with large User Memory (e.g., aviation part tags carrying ATA Spec 2000 data), Block Write is not merely a performance optimisation but a practical necessity. Writing 512 bits (32 words) sequentially would take over 600 ms; Block Write reduces this to under 200 ms.

Verification

After a Block Write, best practice is to issue a Read command to verify that the written data matches the intended payload. This read-after-write verification adds 10-20 ms but catches programming errors caused by weak RF signals, detuning, or marginal tag sensitivity. Most commercial printer-encoder systems perform this verification automatically and mark tags that fail as defective.