Hi Neil
I took a look at the FTDI USB-UART kit.
From what I understand it allows a DIP format module to be located on your board with RS232 (I think at logic level) to be connected to the local processor, where the modul is either supplied locally or powered from the USB bus (when connected).
The processor communicates using normal UART to a host (PC with virtual COM) as if the UART were connected directly to a standard COM port. Possibly the baud rate can also be set a bit higher than a normal COM port as well.
The main advantage that I see of using such a module is that it allows PCs with no COM port to be connected via USB to use typical serial protocols. Of course if the processor can not do USB itself (or the software development investment is too high) it is a practical solution.
I too have a project where I have a serial protocol communicating with a PC program which was developed some time ago. The processor has recently migrated to a SAM7X with integrated USB. This is used to program the boot software (which is practical since it is very fast, a nice 'modern' solution, is in fact cheaper than RS232 since the USB socket on the board costs less that the otherwise necessary RS232 level converter and needs no further components since the USB PHY is also integrated in the chip). Also using USB for communication with the PC program is something which is being talked about.
1. because a lot of new PCs just don't have COM ports any more
2. because it is nice for marketing to write it on their feature list
As I mentioned, I am preparing to integrate a USB stack (initially on the M5222X) into the uTasker project (I have read several books and have several development boards ready and am in the process of ordering a USB analyser) but I don't intend to use it just yet for the PC communication in the SAM7X project. There are 2 main reasons.
1. The cards are in a fairly large machine and have two RS232 interfaces. I will hide a RS232-USB converter (one with a 1m cable and true RS232 which are very cheap in every PC shop) in the machine with a USB socket in the housing. This will allow users with no COM to connect using a straight USB cable (the user could also connect the RS232-USB converter to the RS232 interface if he/she wants) but from a marketing point of view he/she should usually believe that the straight cabel is enough...
2. I use RS232-USB adapters (the cheap ones from the local PC shop) and have found them quite good, but not perfect. Sometimes it is necessary to unplug them and plug them again - one that I have can hang in XOFF mode and then that is the only solution to get it going again. Basically I don't trust USB due to experience with unreliability, whereas the old fashioned COM ports have never given problems.
I believe that the FTDI USB-UART kit can be considered to be equivalent to my USB-RS232 cable (but smaller and located on the board without RS232 converter). I don't know about reliability. Once I understand the details better I hope to have the chance to analyse some of the USB problems that I have encountered to get an idea about where their cause is and whether they are due to bugs in the devices themselves, the host or basic flaws in USB itself.
Regards
Mark
