USB to RS232

Ok, Had a talk with the guy`s and here`s what they would like to see in the end.

• We will also need to produce a prototype PCB in the end. So I like to keep it simple the first go round.
• True simultaneous operation of all ports with buffering and good control of latency.

michaelkellett I like the idea of the FPGA I will look into this. I`m a little worried about the programming I`m not sure we have the skills/knowable at this point to pull this off. Are they easy to program? I have one guy here that is/has some knowledge of them

• If you are more used to processors consider using a fast ARM based part which will be able to do 8 UARTs in software at 9600 baud quite easily.(This was our original idea).

mp2100

Yes we used this version for the first testing and everything worked quite nice.

Ok, Had a talk with the guy`s and here`s what they would like to see in the end.

• We will also need to produce a prototype PCB in the end. So I like to keep it simple the first go round.
• True simultaneous operation of all ports with buffering and good control of latency.

michaelkellett I like the idea of the FPGA I will look into this. I`m a little worried about the programming I`m not sure we have the skills/knowable at this point to pull this off. Are they easy to program? I have one guy here that is/has some knowledge of them

• If you are more used to processors consider using a fast ARM based part which will be able to do 8 UARTs in software at 9600 baud quite easily.(This was our original idea).

mp2100

Yes we used this version for the first testing and everything worked quite nice.

Hello Tom,

I quite like FPGAs - but then that's what I do quite a bit.

If this is a commercial project I could help you with FPGA design for money !

If not, then I'll be able to help a bit on E14 with some advice but in the end you'll need to do the actual work. As FPGA applications go this is not a bad one to start with - nothing too fast or horribly complex.

If you will make a lot of these the cost of the FPGA will be important, if only up to a few hundred then I would look at Lattice XP2 parts or Altera MAX 10, if lots and lots then look at Lattice ice40 parts.

Do you just need RX and TX on the RS232 or do you need some or all of the handshake pins as well ?

MK

Well you have thrown a wrench into my plans.....

But after looking at things a FPGA would be a nice solution that we could use in other applications (RS485 for example)

Im looking at the Lattice XP2.

In the end the circuit will look a little like this.

Sure simplifies what I had already started using the conventional method. This will reduce the cost and IC count for sure.

I`m going to buy the proto board to get things moving. In the background I`ll create the PCB and maybe intigrate the CPU.

Looks like you're making some progress Tom - am I right in thinking you wanted separate grounds though for the serial ports?

If you want isolated ports, I've used onto-isolators in the past for the Tx and Rx signals, and a dc-dc convertor to isolate the power supplies for each channels MAX232 chip. You need to be wary of the speed of signals through the opto-isolators (limited myself to 2400baud once.... don't want anyone to repeat that mistake! ).

TI have done a reference design using a capacitive isolator, and powered that from the RS232 line itself, which might be an interesting read and something to consider - http://www.ti.com/lit/ug/tidu298/tidu298.pdf

A

I think I have one of those dev boards - although with Lattice I usually go straight to a custom pcb because I know the parts quite well.

You'll need a clock and a debugging port (can be used to program it on board as well)  for the FPGA in the final design.

MK