Currency Code, Transaction
What it is
ISO 4217 code of the currency of DE 4 — in practice the numeric code: 840 USD, 978 EUR, 826 GBP.
Example values
840US dollar (exponent 2).392Japanese yen (exponent 0).DE 49 on the wire
Bitmap position
DE 49 is bit 49 of the primary bitmap: byte 7, mask 0x80. A primary bitmap with only DE 49 present reads 0000000000008000 in hex.
Length
DE 49 is fixed length: always 3 characters, with no length prefix. A parser reads exactly that many and moves on, so shorter values are left-aligned and padded with trailing spaces.
Size in the message
At most 3 bytes when the message travels as text (ASCII or EBCDIC).
Format a or n
Format a or n means alphabetic or numeric: a currency code written as letters (USD) or digits (840).
Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.