HP 8753E Programming And Command Reference Manual page 166

Defines 3 bits, DO through D2, on the test
set connector I/O for the channel 1 and
channel 2 forward settings. These bits can
be set to values of 0 through 7. Be careful
that you do not also set a value to ATTPl
and A'ITPB as there is interaction between
these commands and they will change
the values you have set for DO through
Values for ATTPl and ATTPS translate to
the following values for DO through D2:
1-159
HP-IB Progr amming and Command Reference Guide