QuadTech 1865, Инструкция по эксплуатации, Страница: 60 / 87

Page 60 of 87 Operation
Table 2-3 NOTES
* The input signal is active low and requires a positive-voltage external circuit, which
must pull the signal line down below 0.4V, but not less than 0.0V, i.e. not negative. The
logic-low current is 0.4mA (max). For the inactive state (logic high), the external circuit
must pull the signal line above +2.5V, but not above +5V. This can be converted to a
isolated active low input by removing jumper JP3 on the I/O PCB.
** Outputs can be active low optically isolated open - collector drivers that pull each
signal line to IGND (isolated common) when asserted. All outputs require a positive
+5V to +24V external source (referenced to IGND) and pull-up resistor to operate as
fully isolated signals. IGND can be isolated from system GND by removing jumper JP2
on the I/O PCB. With jumper JP2 in place optical isolation is defeated allowing the
outputs to be pulled up to the 5V with external resistors. The outputs can sink up
to 80mA of current. Greater currents can damage the instrument.
*** Pin 34 is connected to the + input of the optical isolator through a 620
Ω
current
limiting resistor. Pin 35 is connected to the - side of the optical isolator. Recommended
force current through this circuit should be between 1 and 5mA nominal (10mA max).
34
35
+
-
pin
pin
ohms
620
start
Figure 2-33: Isolated Connection
2.7.2 IEEE-488 Interface
The IEEE-488 interface is available as an option to the 1865. When this option is present
connection is made through a connector (24 pin) on the rear panel. This interface can be
used to connect to a system containing a number of instruments and a controller in which
each meets IEEE Standard 488.2-1987 (Standard Digital Interface for Programmable
Instrumentation) Refer to Table 2.4 below for a full tabulation of connections and Table
2.5 for the command set.
The following functions have been implemented. Refer to the standard for an
explanation of the function subsets, represented by the identifications below.
SH1 Source Handshake PP1 Parallel Poll AH1 Acceptor Handshake
DC1 Device Clear DT1 Device Trigger SR1 Service Request
RL1 Remote Local L3 Listener C0 Controller
E2 Electrical Interface T5 Talker