Original Data Elements
What it is
Identifies the original transaction in reversals/adjustments: original MTI, STAN, timestamp, acquirer and forwarder IDs.
A 0400 reversal must say what it reverses. DE 90 concatenates five fixed subfields of the original message: MTI (4), STAN (6), transmission date/time (10), acquiring institution ID (11, zero-padded), forwarding institution ID (11, zero-padded). Hosts match this against their transaction log to release the held funds.
Example values
0100 320512 0801143205 00000012345 00000000000Reversing the 0100 with STAN 320512 sent 08-01 14:32:05 by acquirer 12345.DE 90 on the wire
Bitmap position
DE 90 is bit 26 of the secondary bitmap: byte 4, mask 0x40. A secondary bitmap with only DE 90 present reads 0000004000000000 in hex. The secondary bitmap is only sent when bit 1 of the primary bitmap is set, so any message carrying DE 90 has a primary bitmap whose first hex digit is 8 or higher.
Length
DE 90 is fixed length: always 42 digits, with no length prefix. A parser reads exactly that many and moves on, so shorter values are right-aligned and padded with leading zeros.
Size in the message
At most 42 bytes when the message travels as text (ASCII or EBCDIC), or 21 bytes in binary dialects that pack digits as BCD.
Format n
Format n means numeric: the digits 0–9 only.
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.