Interfacing a GPIB Chip to a Microcontroller

[meledson]

Is it possible to "snoop" between the communications of a talker and a listener? It will be listening (will not do any talking) to the communications of the two to gather data. But it will not interfere with the operation of the two.

For example, a DMM is connected to a PC via GPIB doing voltage measurements. The project will tap into the GPIB bus and snoop to the communications of the two to get the voltage readings (data) sent to the PC. We cannot touch the operation og the PC, so the alternative is to get it from the bus. Is this project possible?

The project spces have been changed and I have to do a "GPIB snooper" and will use a 3.3 Volt Rabbit Microcontroler.

[ScottieB]

None of the GPIB chips are really designed to do this.  If you can use our PCI-GPIB+ Analyzer Board, that would be the easiest.  This board has a GPIB chip, but it doesn't use it for snooping.  I believe the analyzer portion of it is mostly in an FPGA. Of course, then, you're tied to using our GPIB Analyzer Software.  I'm not sure if you have custom software requirements.

If you're only interested in snooping data bytes and not commands, I wonder if you could make the TNT4882 or TNT5004 a "listener only" device for every single GPIB address.  You'd probably do it using the "multiple primary address" method outlined in the "Software Considerations" chapter of the TNT4882.  You might check into that, but again, the chips were not intended to be used in this way.

Scott B.

GPIB Software

National Instruments

[meledson]

My Plan A is use a GPIB chip to "snoop". If it is not possible/allowed, my Plan B is to use a fast microcontroller to do the decoding of the GPIB protocol.



Plan B takes a lot of developing time and skill on the Protocol, which I am apprehensive.



I hope some one will point me to the best direction.



Thanks!

Message Edited by meledson on 09-01-2005 12:48 AM

[Collin M]

As Scott said, there is a listen-only mode in all the GPIB ASICs available from NI. One implementation that uses this feature is implementing a single GPIB device that responds to multiple addresses, which is described in the manual for each ASIC. This addressing mode involves manually interpreting each command byte sent by the controller, and then forcing talker or listener mode. For your application I think you only want to listen to data sent by the DMM, correct? In that case you would implement this addressing mode and become a listener whenever the GPIB controller in the PC is addressed to listen.

Have you decided which GPIB ASIC or board you are going to use?

[meledson]

I am planning to use TNT4882 or TNT5002.

I will be using a rabbit microcontroller that uses a 3.3V supply and signaling. But the ports are 5-volt tolerant.

I have presented both plans to my boss and his suggestion is to use a serial-to-GPIB solution for faster deployment. I have a spare serial port on the rabbit, but it only uses TX and RX. I have no hardware handshaking.

[Collin M]

I'm not sure I understand where the serial-to-GPIB solution fits into this. Will the serial port be used to connect the rabbit microcontroller to a PC?

Are you required to use a rabbit microcontroller? Do you want the GPIB data to eventually be on a PC? If so, one possibility is to use a PCI-GPIB and use the NI-488 driver to force the PCI-GPIB into listen-only mode. You could then just do continuous reads with large timeouts.

[meledson]

We are using the Rabbit Microcontroller as the processor of our data gathering box. This box is connected to the company network via embedded ethernet. We will be deploying a few hundred of these boxes for data gathering. Unfortunately in some of the locations uses a GPIB interface in one of the data sources, hence the plan to interface a GPIB chip to the Rabbit MCU. One option was raised that will use a serial-to-GPIB box. This additional box will be controlled by the Rabbit also.

Data gathered by these boxes goes into a server where a separate computer gathers its data to generate reports.

[Collin M]

Have you considered the GPIB-ENET/100? This is a stand-alone ethernet to GPIB converter. I think that you can configure it to be a listen-only device by using the NI-488 driver. That may be easier than designing a new product and firmware.

If you are required to develop a new product and firmware, then you can use either the TNT4882 or TNT5002 with the rabbit microcontroller.

[meledson]

It is definitely easier to use the GPIB-ENET/100. But I think management would go for a cheaper implementation because of the number of units that will be needed. Besides, my salary is a fixed cost, the implementation is not.

The GPIB-ENET/100 costs more than USD 1000.00 each. If we were to do a cheaper implementation, it will not cost us USD 300.00 in my estimate. If we need about 50 units. It's a huge saving, at my expense.

[Collin M]

Ok, I understand your point about cost.

Have you decided which GPIB ASIC to use?