IOtech Digital488OEM - Handshake Hn; Inhibit Qn; Invert in

Digital488 User’s Manual 7-17-01 Command Descriptions, 3-9
Handshake Hn
The Handshake control command enables software control of the handshake lines, independent of any
other I/O operations. When the Digital488 receives a Hn command, the respective handshake line is pulsed
for approximately 50 microseconds. It returns to its steady-state condition after pulsing.
The Invert command may be used to change the active state of any of the handshake lines.
H0
The Clear line is pulsed
H1
The Strobe line is pulsed
H2
The Trigger line is pulsed
Example:
OUTPUT 718;"H1X"
the Strobe line is pulsed
Inhibit Qn
The Inhibit control command allows software control of the Inhibit line, independent of any other
I/O activities. The 'set' and 'clear' levels of the Inhibit line are determined by the Invert command.
Q0
Clear the Inhibit line (return to unasserted state)
Q1
Set the Inhibit line (place in the asserted state)
Example:
CLEAR 718
reset the Digital488
OUTPUT 718;"Q1X"
set the Inhibit line
Invert In
The Invert command is used to change the polarity of the handshake and data lines. At power up all
handshake and control lines are active high (logic one = + 5 volts). The Invert command can selectively
change the polarity of each of the handshake lines, and of the data lines. If multiple Invert commands
are contained within the same string, then an Execute command (X) should be included between each
Invert command. An alternative is to add the values of each Invert command desired, and send one
command with the sum of the desired commands. The Invert commands are ORed together as received.
To delete any one command, it is necessary to program the default mode I0, then reprogram the desired
commands.
I0
All control lines are active high, all data lines are high true
I1
Inhibit output is active low
I2
Trigger output is active low
I4
Data Strobe output is active low
I8
Clear output is active low
I16
Data is low true
I32
EDR input is falling-edge sensitive
I64
Service input is falling-edge sensitive
Example:
CLEAR 718
reset the Digital488
OUTPUT 718;"I32XI64X"
select EDR and Service input as
falling-edge sensitive
Note:
OUTPUT 718;"I96X"
performs the same function as above