Multi-drop network

A possibility is SPI (Serial Peripiheral interface).

Your PC104 will need a separate line for each device select (addressing done in hardware, not part of the data protocol). It's a snap to implement in hardware.

Cheers

PeteS

Forgot to mention that it should have a range of around 5 metres.

TW

So you are looking for > 30 Mbits/s net. It means a wavelength of less than 10 meters for the bit rate (in practical cables less than 7 meters).

The only PC network technologies coming close to the speed are 100 Mbit/s Ethernet and Firewire, but both need hubs.

IMHO, the speed requirement makes it pretty difficult to create a multi-drop network with the requested cable lengths.

You might be able to do it with a high speed card capable of SDLC. This is a token passing protocol, and your devices need to be connected in a ring. Infineon and others have devices that can handle this protocol. AFAICR they should be able to handle the data rate.

Regards Anton Erasmus

How about 10base2 Ethernet?

There seem to be plenty of PC104 cards available.

Are you sure you want PC104 and not PC104+? The PC104 with an ISA bus is going to be a limitation. At least with PC104+ you get a PCI bus.

I've used some of Sealevel.com's PC104 equipment for RS422 on a 20+ node network. They have a new product that supports 10M bps, but not quite your 3Mbyte/sec. ACB-104.ULTRA PC/104-Plus RS-232, RS-422, RS-485, RS-530, RS-530A, V.35 Synchronous Serial Interface (uses Z16C32)

If you can changed to PC104+ with a PCI interface instead of PC104 with an ISA bus, then General Standards.com might have a product that gets close to what you want (only 10Mbits/sec..

The PC104P-SIO4B is a four channel full-duplex RS-422/485 serial board. Each channel can operate up to 10Mbits/s. Up to 32 Kbytes of FIFO buffering for both transmit and receive (256 Kbytes Total FIFOs) data on each channel provides for a smooth and efficient interface between the serial interfaces and the host computer. This product is based on the Zilog© Z16C30© high speed Integrated Universal Serial Controller (USC) which supports Asynchronous, Isochronous, Bisync, Monosync, HDLC, SDLC, External Sync and Nine-Bit protocols. The USC chip provides full duplex operation with baud rate generators, digital phase-locked loop for clock recovery and a full duplex DMA interface. NOTE: some of the documentation for this product is still being updated, so links below may be to documents with similar operation.

Dosen't cut it.

Doh. I misread the OP's requirement as 3Mbits/s.

-- Grant Edwards grante Yow! QUIET!! I'm being at CREATIVE!! Is it GREAT visi.com yet? It's s'posed to SMOKEY THE BEAR...

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Yes. Its an absolute requrement that we be able to transfer 2MByte of data in under a second.=20

TW

Grant

We are currently using 10Base 2. It is pretty much an obsolete technology these days. Most of the major manufacturers have obsoleted their PHYs for it. Designing it into a product that will have a life of

Cheers TW

Considering ISA is classed as a 2MBytes/sec bus (as PC104 = ISA), how are you going to get 3MBytes/sec across?

Personally at these rates either use as someone else has said PC104plus for higher bandwidth.

Then consider 100baseT network and accept the uncertainty factor, or split your 20 nodes into sub-networks of smaller sizes each with its own 'network' interface. Your network interface then can be RS422/485, or other means.

Personally I think you are trying to "fit a quart into a pint pot".

With simple selfmade hardware this specification is doable. As physical medium choose RS422, RS485, LVDS, all on twisted pair. A separate clock line allows synchroneous hardware. As serializer/deserializer, have a look at CPLDs & Serdes.

Rene

Since you don't specify a bus width, have you considered SCSI? Years ago I saw an article in DDJ where somewone had networked a couple of PCs through SCSI. I know the SCSI standard does not support more that 8/16 devices, but you could use the SCSI hardware to implement your own protocol and thus address more that 16 devices.

Meindert

No problem.

Its not a real time issue, its a "20 port switches for industrial temperature ranges cost serious money" issue.

I'm designing down to a price. If it can't be done I'll have to think again.

TW

And developing your own interface from scratch isn't?

Meindert

I've got no interest at all in developing an interface from scratch.Thats why I'm asking here. Although if it meant saving the cost of a 20 port Ethernet switch in each machine I'd give it serious consideration.

TW

TI makes a number of serdes chips.

Maybe IEEE 1399 is an option ? Upto 63 devices may be daisy chained and the data rate is 400Mb/s. Cable length between devices are only upto 4.5m. It looks like one of the variants based on this core technology should handle your requirements.

Regards Anton Erasmus

I recently got a 16port 10/100Mbit Switch at FRYs for 20$, possibly not industrial temperature range.

Rene

Processing power is cheaper than high speed interfaces. Can you compress the data by a factor of 3?