Figure illustrates how to connect the UART interface of the FT232BL to a TTL – RS232 Level Converter I.C. to make a USB to RS232 converter using the popular “213” series of TTL to RS232 level converters. These devices have 4 transmitters and 5 receivers in a 28 LD SSOP package and feature an in-built voltage converter to convert the 5v (nominal) VCC to the +/- 9 volts required by RS232. An important feature of these devices is the SHDN# pin which can power down the device to a low quiescent current during USB suspend mode
The device used in the example is a Sipex SP213EHCA which is capable of RS232 communication at up to 500K baud. If a lower baud rate is acceptable, then several pin compatible alternatives are available such as Sipex SP213ECA , Maxim MAX213CAI and Analog Devices ADM213E which are good for communication at up to 115,200 baud. If a higher baud rate is desired, use a Maxim MAX3245CAI part which is capable of RS232 communication at rates of up to 1M baud. The MAX3245 is not pin compatible with the 213 series devices, also its SHDN pin is active high so connect this to PWREN# instead of SLEEP#.
http://www.ftdichip.com/Documents/DataSheets.htm
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