X'00' to X'7F' are single-byte codes
X'81' to X'9F' are double-byte introducer
X'A1' to X'DF' are single-byte codes
X'E0' to X'FC' are double-byte introducer
In this example, code points such as X'80' are undefined and have no meaning. A code point such as X'81' is recognized as being the first byte of a two-byte code. The second byte can be any of the 256 possible values. Other DBCS code pages have different organizations; each one is structured according to need.
To summarize, MBCS can be viewed as a more generalized form of DBCS, in which sequences of arbitrary length can be defined. SBCS is the simplest of all, in which every sequence is only one byte long.
In TXSeries for Multiplatforms, no difference exists in coding the CICS-supplied program that performs the standard conversions for SBCS, DBCS, or MBCS data.
Cross-language conversion is not possible. Conversions between SBCS and DBCS or MBCS are also not possible.
In the conversions that are listed above, the length of the converted data might differ from the original length because of the insertion and deletion of shift-out (SO) characters and shift-in (SI) characters and the DBCS or MBCS code scheme difference. An SO character is a code extension character that substitutes, for the graphic characters of the standard character set, an alternative set of graphic characters upon which an agreement exists or that has been designated by use of code-extension procedures. An SI character is a code extension character that is used to terminate a sequence that has been introduced by the SO character to make effective the graphic characters of the standard character set.
CICS® does not have the logic to handle any special treatment of data-length changes. For example, 20-byte user data in a 20-byte input buffer might become more than 20 bytes long after conversion, in which case the data might be truncated. The application must compensate for expansion during data conversion. For more information about how to use shift-out/shift-in (SO/SI) characters, refer to the IBM® 3270 Information Display Programmer's Reference.
In transaction routing, 3270 data streams are always flowed across a network in EBCDIC. Routed transaction BMS panels behave in the same way as do ordinary EBCDIC 3270 screens, regardless of the CICS platform or the code page. Therefore, no MBCS-unique considerations are needed for transaction routing.