8.6. IEEE-488 GPIB Communications

MagnaLOAD DC electronic load products are available with an optional IEEE-488 GPIB interface. When specified at time of order, an IEEE-488 GPIB interface module is installed internally, providing an embedded IEEE-488 GPIB port available for communiations. With two UART ports available, RS232 and IEEE-488 GPIB, the one first receiving communications after power on is the port that is activated. Once activated, the other UART port cannot be recognized unless there has been a period of inactivity for 5 minutes. After this period, a new UART port can be recognized by sending communications. The IEEE-488 GPIB terminal, connector JS4, is detailed in

All of the SCPI subsystem commands in the previous section can be initiated using RS232, optional IEEE-488 GPIB (+GPIB), or optional LXI TCP/IP Ethernet (+LXI) communications.

The IEEE-488 standard defines a method for status reporting. As illustrated in [NEED FIGURE], the reporting method uses the IEEE-488 Status Byte (STB). Three bits of this byte are defined as:

  • Master Status Summary (MSS) Bit

  • Event Status Bit (ESB)

  • Message Available (MAV) Bit

The Master Status Summary (MSS) is an unlatched bit. When the Status Byte Register is read using a Status Byte Register query, bit 6 will be 1 if there are any conditions requiring service.

The STB is masked by the Service Request Enable Register (SRE) to allow the user to mask specific or all events from setting the MSS bit to 1. The MSS bit is obtained by logical OR’ing the bits of the enabled Status Byte Register.

The Event Status Bit (ESB) is set when one of the events defined in the Event Status Register (ESR) [REFERENCE ESR TABLE HERE] has occurred. Like the STB, the ESR is masked by the Event Status Enable Register (ESE) to allow the user to mask specific or all events from setting the ESB to 1.

The Message AVailable (MAV) bit is set to 1 when a message is available in the output buffer.

8.6.1. IEEE-488 GPIB Communications with NI MAX

National Instruments offers Measurement and Automation Explorer (MAX), a Graphical User Interface, as a terminal emulation program for configuring an Interchangeable Virtual Instrument (IVI). MAX is usually installed with one of National Instrument’s Application Development Environments such as LabVIEW, Measurement Studio, or with hardware product drivers such as NI-488 and NI-DAQ.

To operate the power supply with MAX, the instrument must first be located for communications. The following steps describe this procedure.

  1. Run the MAX application program.

  2. In the Configuration window, press the + sign to the left of Devices and Interfaces to view the installed devices.

  3. If there is more than one IEEE-488 GPIB device listed, then select the correct GPIB device.

  4. Press Scan for Instruments on the menu bar and wait several seconds.

  5. At least one instrument should appear under the GPIB controller. If no instruments appear, then refer to [REFERENCE PROGRAMMING GPIB SECTION] to verify the correct setup.

  6. On the menu bar, press Communicate with Instrument. The NI-488 Communicator dialog box should appear.

  7. In the NI-488 Communicator dialog box, press the Configure EOS button. The Termination Method dialog box should appear.

  8. Select the option Send EOI at end of Write. Enter 0 into the EOS byte. Press OK.

Pin

Definition

Pin

Definition

1

DIO1/Data line

13

DIO5/Data line

2

DIO2/Data line

14

DIO6/Data line

3

DIO3/Data line

15

DIO7/Data line

4

DIO4/Data line

16

DIO8/Data line

5

EOI/End or Identify

17

REN/Remote Enable

6

DAV/Data Valid

18

DAV/Gnd

7

NRFD/Not Ready for Data

19

NRFD/Gnd

8

NDAC/Not Data Accepted

20

NDAC/Gnd

9

IFC/Interface Clear

21

IFC/Gnd

10

SRQ/Service Request

22

SRQ/Gnd

11

ATN/Attention

23

ATN/Gnd

12

Shield

24

Gnd