ISO 8583 - 如何为带有子字段的字段计算 BCD 值？

Question

Can anyone answer how BCD data is usually calculated for fields what have subfield values?

I don't mean in terms of code, as I have that part nailed down.

What I mean is say I have field X, which is to be sent containing data for 5 sub values. The field is BCD, but would each sub-value be converted to BCD and then appended to field X or would they be added to field X in the clear and then converted as a whole to BCD?

Can't find a clear answer anywhere... not even in the message spec I'm working off of oO

Cheers, Mike K

Answer 1

You have to know the format of field X and the format of subfields. Let me give you an example.

Assuming that you would like to transmit emv data form pos to Host using a field X.
A format for field X is described below.

Length Attribute 3 bytes LLL Length of data to follow
Subfield 1 var bytes First Additional subfield
Subfield 2 var bytes Second Additional subfield
...
Subfield n var bytes nth Additional subfield

The structure of each additional subfield is as follows
Tag Name 2 bytes
Tag Length 1 byte
Tag Value ..bytes

Answer 2

If a field contains subfields, then every subfield is packed or unpacked with its own format.

The subfields should then not be packed or unpacked again.

If a field contains subfields, it is unnecessary to define the format of the field body. However, the field header format (tag or length) can be defined.

The following example contains a field with three subfields

Message Structure:
<f type="VAL" name="Parent" len="21">
    <f type="VAL" name="Child1" bodyPacker="BcdBodyPacker" len="6"/>
    <f type="VAL" name="Child2" bodyPacker="BcdBodyPacker" len="7"/>
    <f type="VAL" name="Child3" bodyPacker="BcdBodyPacker" len="8"/>
</f>

Message data:
<f name="Parent">
    <f name="Child1" val="111111111111"/>
    <f name="Child2" val="22222222222222"/>
    <f name="Child3" val="3333333333333333"/>
</f>

Message bytes in hex:
111111111111222222222222223333333333333333

The source code of the example can be found on GitHub

The iso-8583-packer Java library was used for creation of this example. I am the author of the library.