ISO ISO IEC 21471-2020 pdf free download – Information technology — Automatic identification and data capture techniques — Extended rectangular data matrix (DMRE) bar code symbology specification.
4.3.2Finder pattern
The finder pattern is a perimeter to the data region and is one module wide.Two adjacent sides, the leftand lower sides, forming the L boundary, are solid dark lines; these are used primarily to determinephysical size, orientation and symbol distortion.The two opposite sides are made up of alternatingdark and light modules. These are used primarily to define the cell structure of the symbol, but alsocan assist in determining physical size and distortion.The extent of the quiet zone is indicated by thecorner marks in Figure 1.
4.3.3Symbol sizes and capacities
DMRE code symbols have an even number of rows and an even number of columns.The symbols arerectangular with sizes from8 ×48 to 26×64 not including quiet zones.For all rectangular data matrixcode symbols the upper right corner module is light in the dark on light version (see Figure 1).Thecomplete attributes are given in Table 7.
5DMRE code requirements
5.1 Encoding procedure overview
This subclause provides an overview of the encoding procedure. The following subclauses providemore details.An encoding example for DMRE code is given in AnnexH. The following steps convert userdata to a DMRE code symbol:
Step 1: Data encodation
As DMRE code includes various encodation schemes that allows a defined set of characters to beconverted into codewords more efficiently than the default scheme, analyse the data stream to identifythe variety of different characters to be encoded. Insert additional codewords to switch between theencodation schemes and to perform other functions.Add pad characters as needed to fill the requirednumber of codewords. If the user does not specify the matrix size, then choose the smallest size thataccommodates the data.A complete list of matrix sizes is shown in Table 7.
Step 2: Error checking and correcting codeword generation
Generate the error correction codewords for the result codeword stream from above step. The resultof this process expands the codeword stream by the number of error correction codewords. Place theerror correction codewords after the data codewords.
Step 3: Module placement in matrix
Place the codeword modules in the matrix.Insert the alignment pattern modules, if any, in the matrix.Add the finder pattern modules around the matrix.
NOTE Table 1 of this document is identical to lSO/IEC 16022, Table 1.5.2Data encodation
5.2.1Overview
The data may be encoded using any combination of six encodation schemes(see Table 1). ASCIIencodation is the basic scheme.All other encodation schemes are invoked from AScll encodation andreturn to this scheme. The compaction efficiencies given in Table 1 need to be interpreted carefully.The best scheme for a given set of data may not be the one with the fewest bits per data character.Iifthe highest degree of compaction is required, account has to be taken of switching between encodationschemes and between code sets within an encodation scheme (see AnnexI). lt should also be noted thateven if the number of codewords is minimized, the codeword stream sometimes needs to be expandedto fill a symbol.This fill process is done using pad characters.
5.2.2Default character interpretation
The default character interpretation for character values 0 to 127 shall conform to ISO/IEC 646.Thedefault character interpretation for character values 128 to 255 shall conform to lso 8859-1. Thegraphical representation of data characters shown throughout this document complies with the defaultinterpretation.This interpretation can be changed using extended channel interpretation(ECI) escapesequences, see 5.4. The default interpretation corresponds to ECl 000003.
5.2.3ASCIl encodation
ASCll encodation is the default encodation scheme for the first symbol character in all symbol sizes. ltencodes ASCll data, double density numeric data and symbology control characters. Symbology controlcharacters include function characters, the pad character and the switches to other code sets.AScIIdata is encoded as codewords 1 to 128 (AScll value plus 1).Extended ASCll (data values 128 to 255)is encoded using the upper shift symbology control character (see 5.2.4.3).The digit pairs 00 to 99 areencoded with codewords 130 to 229 (numeric value plus 130).The ASCIl code assignments are shownin Table 2.ISO ISO IEC 21471 pdf download.