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Kepco's Digital Highway VXI Logo

Modern desk-top computers typically support one or both of the instrument-control buses: RS 232 and IEEE 488.2. Many Kepco power supplies directly communicate with these two digital highways. Their limitations, however, in terms of the number of instruments supported and the distance that can be covered, have led Kepco to adopt a third digital bus to distribute signals to its power supplies.

We chose the IEEE 1118 bus that originated as Intel's BITBUS as our serial communications link. By choosing a 375KHz data rate and limiting it to 27 talk-listen power supplies, we are able to provide communications to our power supplies over a 300m (1000') path. The operation of this serial link is entirely transparent to users. The communication from PC to the IEEE 488.2 bus to Kepco IEEE 1118 bus to power supply and back is exactly as if the PC were talking to the power supply on the IEEE 488.2 bus alone. The difference is that there can be 27 power supplies spread over 300m of a daisy chained two-wire serial bus.

Digital Highway

(For further information about any of the Kepco products shown above, click on either the name or illustration of the product.)

The illustration above shows some of the hardware that Kepco offers to facilitate communications between desk top computers and their common instrumentation buses and Kepco's power supplies. To the right are PC and MAC type computers with assumed drivers to link them to both RS 232 and IEEE 488.2 buses. In the center are interfaces that can be used to relay information from either of these buses to the Kepco serial bus, IEEE 1118.

From the top:

An MBT power supply with the "G" option. The "G" option is a single board computer (SBC) installed within the MBT that handles communication between either IEEE 488.2 or RS 232 and itself. The SBC can relay two way communication, via the serial bus, to 26 more models of all types. MBT's SBC supports CIIL and SCPI.

Next is model TMA 4882-27, a 1U (1-3/4") high rack mount instrument that supports the SCPI and CIIL languages from IEEE 488.2 or RS 232 and simply translates them to and from the IEEE 1118 serial bus. It is not, itself, a power supply.

The next interface is called MST 488-27 . It is a plug-in assembly for an MST rack (RA 55) that provides an IEEE 488.2 or RS 232 input to the whole rack (8 MST-type power supplies). It can also support as many as 19 more power supplies of all types via the IEEE 1118 serial bus.

Lastly, we illustrate a VXI card cage which can communicate with IEEE 488.2 (GPIB). A Kepco interface, TMA VXI-27 plugs into a single width size C slot and provides support for up to 27 power supplies via our serial link.

On the left are Kepco power supplies that can communicate in one or more of these modes. On the top left is our DPS, a bench-type 75W model which incorporates an RS 232 port. Below it is illustrated an MBT power supply without the single board computer (non-G). These models can communicate with the host computer via the serial link no matter which interface is providing the connection.

Below the MBT is a rack full of MST plug-in power supplies without the MST 488-27 interface. This rack, with nine (9) plug-in modules can be driven by any of the GPIB-to-IEEE 1118 interfaces. Up to 3 racks with 9 modules (27 power supplies) can be supported from a single GPIB address.

The MAT models illustrated below the MST are able to link to the IEEE 1118 serial bus to communicate with a host PC or MAC, via any of the interfaces. MAT are available in three sizes: 360W (illustrated), 720W and 1080W.

Kepco's BOP series bipolar power supplies have an open digital slot. Two plug-in cards are made to fit this slot. The BIT TMA-27 links BOP to the IEEE 1118 serial bus just like MAT, MST and MBT. With the serial card, BIT TMA-27, the BOP are included among the up to 27 models that can be daisy-chained together to share a single GPIB address. Model BIT 4886 , is a card that allows BOP to link directly to the IEEE 488.2 instrument bus. This link would be useful for short range communication involving just one or two BOP. Model BIT 232 allows BOP to link directly to the RS 232 communication bus. NOTE: Although the diagram shows both an RS 232 and IEEE 488.2 card, the BOP accommodates just one BIT card.

Contact Kepco, Inc. for more information or to get a copy of our latest catalog.

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