Amount, Cardholder Billing Fee
What it is
Fee charged to the cardholder, in the cardholder billing currency (DE 51). Rarely used.
DE 8 on the wire
Bitmap position
DE 8 is bit 8 of the primary bitmap: byte 1, mask 0x01. A primary bitmap with only DE 8 present reads 0100000000000000 in hex.
Length
DE 8 is fixed length: always 8 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 8 bytes when the message travels as text (ASCII or EBCDIC), or 4 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.