USB to 9-Pin Serial Conversion

[Jake M]

No, I'm not talking about the USB Dongle.

I spent a week in Rolla over last summer for an Intro to Engineering Camp and in the Computer Engineering presentation, I got a small 3''x3'' circuit board with a cheap little microprocessor built in. The IO consists simply of four switches, four LEDs and a basic speaker. I'm going to replicate it a few times so each of our prospective programmers for next year can play around with them and get a feel for how microcontrollers work. The board utilizes a 9-pin serial port for program loading, much like the FIRST RC. Our school provides laptops for every student (except our Senior class. We were the last class to not get them), but none of them have a 9-pin serial port.

I know the basic background of how the 9-pin serial port works (RS232, I believe. Correct me if I'm wrong), but USB is very sketchy. I figured someone around here knows enough to help me. Am I correct in saying that USB is basically a 4 pin serial port that uses a +5V pin, a Tx pin, an Rx pin, and a Ground pin? If so, could I make a custom cable that wires the USB's Tx to the 9-Pin's Rx (In addition to using 9-pin serial, the board is designed so that you have to use a Null-Modem cable), and so forth?

RS232        USB
-----        ---
1:DCD        +5V
2:RxD--------Data-
3:TxD--------Data+
4:DTR      |-Gnd
5:Gnd------|
6:DSR
7:RTS
8:CTS
9:RI

I'm just hoping I don't have to actually go out and buy USB to 9-Pin Serial converters for everyone. I bought one for myself a while back, before I knew a whole lot about this stuff (though I still don't), and if I remember correctly, buying one for every member might get expensive.

[Kevin Watson]

Originally Posted by Jake M

I'm just hoping I don't have to actually go out and buy USB to 9-Pin Serial converters for everyone.

Sorry to be the bearer of bad news, but you do. There is no easy way to connect a RS232 device to your laptop's USB (you may very well frag something if you wire it up per your diagram).

-Kevin

[Jake M]

Kinda thought so.

At the least, can anyone explain how USB actually does work?

[DonRotolo]

There are lots of resources online to tell you that.

What is important here is that RS-232 uses +12 and -12 volts for signaling, while USB does not. RS-232 uses one wire for "transmit" and one wire for "receive", USB uses two wires as a differential pair much like CAN Bus.

So yes, you need those converters.

[jzampier]

The USB specification is IIR freely available (and several hundred pages). There is quite a bit that goes on at the MAC and PHY levels which software does not, typically, have control over. RS232 has none of that.

I recommend a little dongle. Blackbox makes some nice multi-port ones, as do other companies. I'd avoid anything with a prolific chipset, the FTDI chipset is better.

Hobby Engineering, http://www.hobbyengineering.com
Sells some modules for integration if you are interested. I've used them for projects before and they work pretty well. Drivers for windows and linux.

[hipsterjr]

I broke down and had to buy one yesterday. We have had to use a Pentium 2 since 2000 to program our bot simply b/c of the serial port.! It cost me $36.99 at BestBuy.

[mormannoob]

Any word if IFIs new controllers are still serial or not

[Kingofl337]

From what I've heard IFI is not providing the new controller(s)

But IFI plans to release a WIFI Vex Controller

[Kevin Watson]

Originally Posted by Kingofl337

From what I've heard IFI is not providing the new controller(s)

From what I've heard, Intelitek has signed a non-disclosure agreement that states they won't discuss anything related to the new control system with outside parties.

-Kevin

[Kingofl337]

Anything I have heard has been on these threads...

I have heard nothing as far as intelitek is concerned, if that is incorrect I'll gladly remove it....

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