Thank you for your answer. But I saw an artical provided by Maxim-IC, named'Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards'.

In this artical, it says:'The RS-232 link was initially intended to support modem and printer applications on IBM PCs, however, it now enables a variety of peripherals to communicate with PCs. The RS-232 standard was defined as a single-ended standard for increasing serial-communication distances at low baud rates (. There are really two questions here: What is the highest baud rate per the standard? What is the highest baud rate you can actually use? RS-232 is an old standard, and IMHO it was pretty conservative for it's day. I'm not at work now, or I'd have the right book at hand to give you the numbers.

The cable length was rather short, and the speed rather low. The standard does give absolute limits, and technically if you're operating outside that, you're not doing 'RS-232', you're doing something else. There were other newer standards for serial as well, with higher rates. Again, book not in reach. To the second question, there are some limiting factors. The driver chips will have slew rate limits, the cable capacitance per foot will factor in, and the devices themselves will contribute some error as their baud rate divisors get smaller, unless they are using one of the baud-rate multiple crystals, usually an integer multiple of 3.585 MHz. So to this question, the simple answer is 'crank it up till it breaks, then back off a bit'.:).

Clawson wrote: I think 3.6864 is only a common choice because it's a common video timebase too. Common in what way? Just curious because I have never heard of anything video related with 3.6864MHz, and I work very closely with video related stuff. But to the original question, there is no limit, or yes there is but it depends on what kind of devices are communicating together and how far apart they are. Most PCs go up to 115200 normally, but most PCs have chipsets that could be set to faster speeds with proper drivers.

The maximum Baud rate achieveable with FTDI's current devices is 3M Baud. This can be set or adjusted by setting a Baud rate divisor using the FT_SetDivisor function. The baud rate. This parameter specifies the number of bits per second that a serial port is currently configured to transmit or receive. For example, a BaudRate value of 115200 indicates that the port is configured to transfer 115,200 bits per second.

Jun 19, 2008 The following baud rate values are valid: 110, 300, 600, 1200, 2400, 4800, 9600 (default), 14400, 19200, 28800, 38400, 56000, 57600, 115200, 128000, 256000. PortOpen The PortOpen property specifies a logical value that controls whether or not the serial port is open and active.

The limit is historical, and comes from the fact that they used 1.8432MHz crystal in the original PC serial ports. Also the PCI cards with their drivers can go maybe up to 1 megabit or 960kbit. USB serial ports go up to 3 megabits. The real difference is what kind of level shifter you have there, some el cheapo level converters are only specified to pass 115200 adequately. There may be other limits like how fast rise/fall time the signal is specified to have, or how slow it can be due to weak drivers or bus capacitance from long wires. Heck, there are even some USB RS232 adapters that claim to go up to 460kbps but you can see through the transparent case that it has a level converter chip specified to only 250kbps.

I trust only FTDI cables. Jepael wrote: Just curious because I have never heard of anything video related with 3.6864MHz, and I work very closely with video related stuff. I think he was getting confused with the NTSC colorburst frequency of 3.5795MHz. Xadrez Master 5.8.6.0 Serial. [I quite often make the same mistake] Not sure why 3.6864MHz is a popular frequency other than it being twice the nominal 1.8432MHz UART clock, allowing for 230.4Kbps transmissions, where the 1.8432MHz clock limits at 115.2Kbps.

Maybe also because it is relatively close to 4MHz, which may have been a common frequency limit for micros at some point. Quote: Hi,all, I am using RS232 serial communication to send data to PC. The IC I am using for signal level adjusting is MAX232A. Now I am a bit confusing about the baudrate.

I saw that the maximum transmission speed of RS232 is 20kbps. Does that mean my baudrate can not higher than this speed? If yes, why MAX232A chips can have a maximum data rate of 200kbps?