MicroPDF417 (^BF) - Barcode Reference

What is MicroPDF417?

MicroPDF417 is the compact variant of PDF417, defined in ISO/IEC 24728. It reuses PDF417's 929-codeword set, the same three data compaction modes (Text, Byte, Numeric), and the same Reed-Solomon arithmetic over GF(929) - but lays them out in a smaller frame by omitting PDF417's row-indicator codewords and replacing the start/stop patterns with a more compact Row Address Pattern (RAP) system.

A MicroPDF417 symbol carries one of 38 fixed configurations: 1, 2, 3, or 4 columns wide; row counts from 4 (4-column variants) up to 44. The encoder picks the smallest variant whose capacity (data codewords + ECC codewords) holds the payload; the decoder reads the variant directly from the RAP indicators it sees, with no separate "version" field to encode.

Used for: healthcare equipment serialisation (DoD UID-2, medical-device UDI), electronics direct part marking on components too small for a full PDF417, postal applications where a narrow stacked code fits alongside printed text, and as the 2D half of the TLC39 composite (a Code 39 linear paired with a MicroPDF417 for telecom equipment labelling).

How it differs from full PDF417

Feature	Full PDF417	MicroPDF417
Standard	ISO/IEC 15438	ISO/IEC 24728
Columns	1 to 30 (data columns), continuous range	1, 2, 3, or 4 only
Rows	3 to 90 (continuous)	4 to 44 (38 fixed configurations)
Row indicator codewords	Yes - two per row (left + right) encode row#, column count, ECC level	None - that information is in the RAP itself
Start / stop patterns	Fixed start and stop patterns at row edges	Left RAP + Right RAP per row (+ Centre RAP on 3- and 4-column variants)
Codeword width	17 modules (4 bars + 4 spaces)	17 modules (4 bars + 4 spaces) - identical
Codeword set	929 codewords (0–928)	929 codewords (0–928) - identical
Compaction modes	Text / Byte / Numeric	Text / Byte / Numeric - identical
Error correction	RS over GF(929), ECC levels 0–8 (2 to 512 ECC codewords)	RS over GF(929), per-variant fixed ECC count (typically 6–32)
Quiet zone	≥ 2× X-dimension on all sides	≥ 1× X-dimension on all sides
Smallest dense payload	3 cols × 3 rows = 9 codewords (minus row-indicator overhead)	1 col × 11 rows = 11 codewords; 4 cols × 4 rows = 16 codewords

The two row-indicator codewords PDF417 spends on each row encode the same three pieces of information for every row (row#, column count, ECC level). MicroPDF417 moves all three into the RAP pattern selection, so every row's full width is available for data + ECC. This is what makes 1- and 2-column variants viable in MicroPDF417: in full PDF417 the row-indicator overhead would dominate.

Where it's used

TLC39 composite: the telecom-industry composite code pairs a Code 39 linear (the ECI number) with a MicroPDF417 (additional structured data). See TLC39 for the linkage rules.
Healthcare and pharma: medical-device UDI labels under 21 CFR Part 830 frequently use MicroPDF417 for the production identifiers (serial, lot, expiration) when a full PDF417 won't fit.
Direct part marking (DPM): electronics components, ammunition, surgical instruments - any application where a stacked 2D code is acceptable but full PDF417 is too wide.
ZPL output: Zebra printer command ^BF produces MicroPDF417 (distinct from ^B7's full PDF417). TSPL exposes it via the top-level MICROPDF command or (model-dependent) as a BARCODE "MICROPDF" type.

Construction

New to these terms? module , quiet zone , X-dimension , symbology - the linked pages cover each one from first principles.

Symbol structure

Every MicroPDF417 row is laid out as:

[Left RAP] [Column 1 codeword] [Column 2 codeword] {[Centre RAP]} [Column 3] [Column 4] [Right RAP]

The centre RAP is only present on 3- and 4-column variants (between columns 2 and 3). Each codeword is exactly 17 modules wide × 1 module tall, with 4 bars and 4 spaces. A row's total module width is therefore:

1-column variant: 10 (Left RAP) + 17 (codeword) + 10 (Right RAP) = 37 modules
2-column variant: 10 + 17 + 17 + 10 = 54 modules
3-column variant: 10 + 17 + 17 + 10 (Centre RAP) + 17 + 10 = 81 modules
4-column variant: 10 + 17 + 17 + 10 + 17 + 17 + 10 = 98 modules

RAP patterns are 10 modules wide. The centre RAP exists to give the decoder a synchronisation point in wider rows, mirroring the role full PDF417's row indicators play.

The 38 variant configurations

MicroPDF417 has exactly 38 fixed (columns × rows) configurations, indexed from 1 to 38 in the encoder's lookup table. Each entry specifies four numbers: the column count, the row count, the data codeword capacity, and the number of Reed-Solomon ECC codewords appended after the data. ISO/IEC 24728 Table 3 lists them in full.

Columns	Variants	Row count range	Total codewords	Notes
1	11	11 – 44	4 – 38	Tallest, narrowest aspect ratio. The 1×11 minimum is the smallest MicroPDF417 symbol.
2	11	8 – 44	8 – 76	Most common choice when a label is wider than tall.
3	9	6 – 44	12 – 114	Introduces the centre RAP between columns 2 and 3.
4	7	4 – 44	20 – 152	Widest aspect; the 4×4 variant is the smallest dense payload.

The encoder selects the variant with the smallest total codeword count that can hold (compacted data + chosen ECC count). For the per-variant data/ECC split, see ISO/IEC 24728:2006 Table 3; it is reproduced verbatim by every conforming encoder.

Codeword set (shared with PDF417)

MicroPDF417 reuses PDF417's 929-codeword alphabet. Each codeword is one of three clusters, with clusters cycling by row number:

Cluster 0 - used for rows where row % 3 == 0
Cluster 3 - used for rows where row % 3 == 1
Cluster 6 - used for rows where row % 3 == 2

Each cluster has 929 distinct 17-module patterns mapped to codeword values 0–928. The cluster of any codeword in a printed symbol identifies the row modulo 3, which the decoder uses to validate row order. The lookup tables (one per cluster, 929 entries each) are in ISO/IEC 15438:2015 Annex B and are inherited unchanged by ISO/IEC 24728.

Data compaction

The three compaction modes are identical to PDF417:

Text compaction - packs 2 characters per codeword from a 30-character sub-alphabet (Alpha, Lower, Mixed, Punctuation sub-modes; the encoder emits explicit latch/shift codewords to switch). Densest for ASCII text payloads.
Byte compaction - packs 6 bytes into 5 codewords using base-900 arithmetic; the remaining 0–5 bytes (if any) are emitted one codeword per byte. Used for arbitrary binary payloads.
Numeric compaction - packs 44 digits into 15 codewords using base-900 arithmetic with a leading "1" sentinel. Densest by far for all-digit payloads (about 2.93 digits per codeword vs Text mode's ~1 digit per codeword via the Mixed sub-mode).

The encoder may mix modes within a single symbol via explicit latch codewords. The first data codeword is implicitly Text mode unless an initial latch is emitted.

Reed-Solomon error correction

MicroPDF417 uses Reed-Solomon over GF(929) - the same finite field as PDF417. The primitive element is 3, and the generator polynomial for an n-codeword ECC block is g(x) = ∏(x − 3ⁱ) for i = 1..n, all arithmetic modulo 929.

The number of ECC codewords is fixed per variant (not configurable like PDF417's ECC levels) and ranges from 6 to 32 codewords across the 38 variants. The error-correction capacity is ⌊n / 2⌋ − 1 codewords, with the remaining capacity used for erasure correction.

ECC codewords are appended at the end of the data stream and laid out continuously across rows along with the data - no interleaving (the symbols are small enough that interleaving brings no benefit).

Quiet zone and X-dimension

MicroPDF417 requires only 1× X-dimension of quiet zone on all four sides (full PDF417 requires 2×). Combined with the absence of row-indicator overhead, the result is meaningfully smaller printed symbols for the same data payload. A 2×11 MicroPDF417 with light ECC at 0.17 mm X-dimension occupies roughly 9 × 2 mm - small enough for an electronics-component label that a full PDF417 cannot fit.

MicroPDF417