Data Encoding and Representation

This section describes the attributes of Elavon ISO-8583 message fields.

Attribute

Description

N x

x numeric digits, BCD encoded, right justified with leading half bytes zero filled

b x

x bits in a bit-field (8 bits per byte; all combinations hex00 to hex FF are allowed)

an x

x alphabetic and numeric characters

ans x

x alphabetic, numeric and special characters

a x

x alphabetic characters

x+N 16

Prefix "C" (credit) or "D" (debit) followed by N 16 field

LL, (LLL)

2 (or 3) digit length, BCD encoded, of variable length field following

VAR y..x

variable length field of type y - maximum size x

Numeric Data

Numeric data (type N x or VAR N) is represented as packed BCD - that is two BCD digits ('0', '1' '9') are stored in each byte. The first digit is stored in the upper nibble and the second digit in the lower nibble.

If the length of the data is odd, it is padded by adding a nibble 0 (zero) to the left of the number. This hex '0' for padding ensures that a whole number of bytes are used for the field and is not included in the length of the item.

Alphanumeric Data

Attribute

Description

a

('a', . . . 'z', 'A' . . . 'Z')

an

('a', . . . 'z', 'A' . . . 'Z', '0' . . . '9')

ans

(hex 20 to hex 7F)

 

Alphanumeric fields should be left justified with trailing spaces.

LLVAR Variable Length Data

All LLVAR variables irrespective of their type are preceded by two bytes which contain the length of the data represented as two bytes of BCD data (right-justified with leading 0 as necessary). The most significant digit appears first in the message. The length indicates the number of bytes of the data element.

Bitmap Fields

Data elements are counted from left to right - that is, from most to least significant, with the left most bit position representing field number 1. The bitmap field will always contain either 8 or 16 bytes, with bytes 9 to 16 present if and only if the most significant bit of byte 1 is set.