HP 61010A Owner's Manual page 51

Output). Notice that some of the software formatting and
hardware features are common to both the Digital Input
and Digital Output. Because the Digital Input and Digital
Output functions are independent of each other, you must
specify whether you are programming either the Digital
Input or the Digital Output by supplying the correct label
after each statement. This is especially true when
programming common features.
Some programming statements control functions that are
specific to either the Digital Input or the Digital Output.
For example, the MEASURE statement programs only the
input register to read the data on the input bits. The
OUTPUT statement loads only the output register with
data. If the output driver is enabled by an
ENABLE.OUTPUT statement, the output bits are set.
When the Digital I/O is operated synchronously, the
ENABLE.HANDSHAKE statement activates the handshake
control of either the Digital Input or the Digital Output.
When the handshake control is enabled, the status of the
control signals determines when data is either read by a
MEASURE statement or sent by an OUTPUT statement.
The CHECK.DONE statement checks the status of the
control signals to determine if a handshake is in progress
for either the Digital Input or the Digital Output. The
INITIALIZE statement (not shown) sets the software
functions and hardware registers for the Digital Input or
the Digital Output according to a previously assigned State
file.
Programming With BASIC 5-3