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Modem Programming
Serial port
RS232 Hardware
  Bit Rates

The main feature of iterchange via the serial port is the baud rates. The baud rates is based on the minimum 300 bps (bits per second) baud rates. Also slower (50, 100 and 150 bps) rates can be used, but they are not used in modern technologies. To achieve a high baud rate you simply double the preceding rate, by this getting the following set of rates - 600, 1200, 2400, 4800, 9600, 19200 and 38400, the last rate is the fastest one and is included into new BIOS. Mind that a few years ago the baud rate was only 19200 bps. These rates were limited as the CPU carried out the managing procedures from programme control. Today all new systems use the advantages of Micro Channel, EISA, VL Bus and PCI motherboards,as well as of bus mastering DMA control, which raised the rates of interaction with RAM without using the processor. So when directly managing the hardware you can achieve baud rates up to 155200 bps and above. When introducing new intelligent ports you can get high rates without using the hardware acceleration. These rates are present in new fast modems. But all these rate changes are connected with the introducion of new Universal Serial Bus standard.

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