I have been trying to establish connection between my PC and uC development kit over serial line. There is a standard serial port on the development kit. In oposite there is only USB ports on my laptop. So I have used USB to serial cable for the connection. The problem is that I am not sure whether it is a so called null-modem cable. Can anybody more experienced tell me how to double check it? Thanks in advance.
Electrical – How to recognize USB to RS232 null modem cable
embeddedmicrocontrollerrs232usb
Related Solutions
A1: By far the quickest and easiest method, and possibly the equal best, is to buy an existing USB to serial converter. I've seen these advertised on ebay for under $5 and those were probably not the cheapest. Here are ebay's listings of USB to RS232 converters - well worth looking at to see the range available (and prices).
Wow! - here is one for $US3 including shipping to the US from Hong Kong.
OK - checks - you're in Mumbai, India - checks - $US1.99 to India, free shipping!. You won't build one for that little - probably by a factor of 10 to 20!
Here are a few dozen photos and links to serial to USB converers - hover over the pictures for more information (on the page linked to above - not on the picture below) - click to go to the related site. A few examples - lots of choice !!! -
You can build your own using any of several available custom ICs created for this purpose - but doing that will cost you more than buying a prebuilt one.
A market leader but not the only source of ICs is FTDI corp who make these products.
A2. The most common units (usually a "cable" that plugs into a USB port) appear to a PC as a standard serial "comms port". They work across a range of baud rates. May be manufacturer dependant. Will be settable in software.
A3: As above - appears as a standard serial port.
A4: Some manufacturers peripherals do strange things and may not work for all converters. For example the PIC based PICAxe system uses a programming protocol that sends all data to and fro using RS232 "break signals". ie they do not use the data lines for information transfer. Some converters do not support the break signal.
You will need to know if your equipment is grossly non standard. If it is, some converters may work with it.
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From memory, the Brevia happens to have its connector backwards; it has a female connector, like DCE such as modems, but the wiring is in DTE order. The simple solution is to use the included null modem cable (it looks like an extension cable but swaps pins 2 and 3) with a common USB to RS-232 adapter.
The FTDI breakout module uses LVCMOS levels (1=3.3V, 0=0V) rather than RS-232 levels which are a much wider range), and is missing the level shifting part (U3 on the Brevia). You could use it with other general I/Os by changing the pin mappings in the FPGA design. Just edit the pin constraints for your FPGA design and map the RS232_[RT]x_TTL signals elsewhere; I/O pins are equal as far as the FPGA is concerned, aside from a few dedicated to clocks, reset signals or configuration.
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Best Answer
It would be very unusual for it to be a null-modem cable. A USB to serial converter normally allows you to add a serial port that is connected in, and works in the same way as the original COM ports fitted to desktop PCs. You would use a null-modem cable to connect, for instance, two PCs together.
If you would need a null-modem cable to connect your development kit to a desktop, you would also need one to connect to your USB converter.