Measurement Computing Digital488 - Manual (Page 34)

Section 3 Command Descriptions
3.4
Bus Input/Output Gn
The Bus Output command determines whether input port data, output port data
or both will be transmitted on the bus when the Digital488 is addressed to talk. The
amount of data sent is dependent on the Pn command.
The G0 default mode causes all input and output port data to be sent to the
controller when addressed to talk. The G1 mode causes only data from the ports
programmed as inputs to be returned when addressed to talk. The G2 mode causes only
data from ports programmed as outputs to be returned when addressed to talk.
If all ports are programmed as outputs with G1 selected and the Digital488 is
addressed to talk, nothing will be transmitted and the bus will hang. The converse will
also cause the bus to hang with all ports programmed as inputs and G2 selected.
G0 Input and output port data is send on talk
G1 Only input port data is sent on talk
G2 Only output port data is sent on talk
Example:
CLEAR 718 reset the Digital488
OUTPUT 718;"P0C1X" port1 as output, ports 2-5 as input
OUTPUT 718;"G1X" select only input ports
ENTER 718; A$ read data from the input ports
DISP A$ display shows FFFFFFFF (data is
dependent on what is connected.
OUTPUT 718;"G2X" select output ports
ENTER 718; A$ read data from the output ports
DISP A$ display shows 00 (outputs default to 0)