How to determine if Use Declare/Fetch is in use by looking at CX= values in connection string

I'm trying to reliably determine whether Use Declare/Fetch cursors
(Abbreviation: B6) is in use for a given DSN based on how my program sees
the connection string. Unfortunately the B6 value doesn't show--but it
appears if I could properly decode the CX= piece I can determine whether
Use Declare/Fetch is active.

Here is an example string returned by my app:
DSN=psql-mydsn;DATABASE=mydb;SERVER=localhost;PORT=5432;UID=postgres;PWD=mypassword;CA=d;A6=;A7=100;A8=4096;B0=255;B1=8190;BI=0;C2=dd_;;CX=1b543b8;A1=7.4-1

for the above dsn I set to use defaults, then just set the UseDeclare
Fetch in the system dsn.

Other examples for CX=
CX=1b503ba (all defaults--Use Declare/Fetch disabled by default)
CX=1b547ba (all defaults, but CommLog set to record)
CX=1b40b0 (all check boxes unchecked, except Use Declare/Fetch is
checked--note this example has one less hex character--I'm thinking maybe
a leading 0 is ignored, but not sure for which pair (1b, 40, or b0).

I looked at the source, but it would take me a while to decipher this--I
was hoping somebody might have a hint.

Thanks...jack