Abstract : FT2232C is a USB to UART / FIFO circuit. In this paper FT2232C features , working principle and applications , given the circuit in a variety of occasions, the typical application circuit . Keywords : Universal Serial Bus ; Universal Asynchronous Receiver Mode / FIFO ; FT2232C Introduction Conducting outdoor information collection , the need for positioning and communication , but also by the various sensor information collection , and therefore require multiple serial ports . Serial port expansion system development has become a frequently encountered problem. General solution is useful to increase the serial port expansion circuit . However, this method uses the circuit more complex circuit , and the serial device connected to plug in when inconvenient to use . This paper presents a new type circuit function FT2232C special chip and used to carry out serial port expansion . FT2232C Introduction 1.1 Circuit Overview FT2232C is a USB to UART / FIFO conversion circuit , is the company following the second generation FTDI FT232BM, FT245BM after the third generation , integrates two BM chip features. Circuit to use 48-LD LQFP package . FT2232C with two multi-purpose UART / FIFO controller were configured into different modes. Downstream of a USB port into two I / O channels , each I / O channel quite a FT232BM or FT245BM, can be individually configured as UART interface, FIFO interface, or . External EEPROM through the configuration , FT2232C also offers a range of new modes of operation , such as multi-protocol synchronous serial interface, which is designed for synchronous serial protocols such as JTAG and SPI bus design. There are synchronous bit width mode , CPU -style FIFO mode , multi-protocol synchronous serial computer interface mode , MCU host bus speed of light competition model and serial computer interface isolation mode . In addition, the circuit 's driving capability has greatly improved , compared to the output circuit is usually 3 times the power , which makes multiple circuits may share the bus . Provided using the FTDI virtual serial port (VCP) drivers , on the external interface to use as a standard serial port using the same PC . Many existing software after a simple reconfiguration of virtual serial port connecting the Cape with the application and circuit communication between the PC 's COM port communication with the same . 1.2 The characteristics of the circuit ? Just add a simple circuit configuration can be achieved by a single circuit to a dual channel serial / parallel conversion ; ? chip handling all the USB protocol , use no additional write USB firmware ; ? 2 -I / O channels (A / B) are independent, can be configured as two 5V, 2?3.3V or a 5V, a 3.3V logic I / O interface; ? UART interface supports 7 or 8 data bits , 1 / 2 stop bit , odd parity / even parity / flag / space / no parity ; ? send a data rate of 300 ~ 1Mb / s (RS-232) or 3Mbs (TTL, RS-232/RS-485); ? Interface mode and USB description of characters can be configured in the external EEPROM , but also on the board of the EEPROM configuration via USB ; ? 4.35V ~ 5.25V in single- voltage range . Simplified Functional Block Diagram 1.3 FT2232C simplified functional block diagram shown in Figure 1 , the unit functions as follows : USB transceiver module : provide USB1.1, USB2.0 full-speed cable to the USB physical interface . A differential transceiver and the end of two separate USB transceiver provides data entry , SEO and USB Reset condition detection . USB DPLL cell : tracking the input NRZI USB data and recovered clock and data signals separately SIE module . SIE modules: implementation of the USB data from serial to parallel and parallel to serial conversion. USB PE modules: management control from the USB end of the data received to deal with low-level USB USB master agreement issued by the request and UART / FIFO controller to issue control commands . RX Buffer and TX Buffer were 384 and 128 byte receive buffer bytes of send buffer . 1.4 Applications The integration of the two functions of the second generation of BM , so FT2232C of a wide range of applications . Mainly converted to two- port USB RS-232, USB converted to dual serial RS-422/RS-485, USB JTAG programming , USB converted to SPI bus interface , on-site can be upgraded with a USB interface, USB products and the exchange of isolated products . 2 FT2232C application example In practice , due to expansion of the traditional serial method is relatively cumbersome , so you can use the circuit to extend the serial port , to achieve when only a simple external circuit can be configured by the USB converter from a two COPMPORT. Specific configuration of the circuit shown in Figure 2 . Design is to note the following: First of all : FT2232C the USBDP, USBDM two input resistor resistance must be equal , a typical value of 27O, and must be 1% precision resistors , or likely to cause the circuit input impedance does not match the Ershi not work . Second : The crystal oscillator circuit at both ends of the two capacitors of capacitance must also be equal, a typical value of 27pF. As the design is to get two serial ports , so plug- in EEPROM can not answer , but directly FT2232C the EEDATA end received through the 10kO resistor on the VCC . In this way FT2232C reset the EEPROM can not be read from the external information , work in default mode, the default circuit , from USB to dual serial port converter . Will be the two serial ports through the circuit VCCIOA, VCCIOB configuration , will VCCIOA then 3.3V, VCCIOB accept 5V, so get the serial port A working voltage of 3.3V, the serial port B of the working voltage is 5V, 3.3V can be connected separately And 5V devices . As RS232 level generally -9V ~ +9 V, and FT2232C conversion received before the need for two serial communication through V or 3.3V, so with the RS232 serial communication needs through the level before the conversion . To SP213EHCA level conversion circuit , for example, the specific circuit shown in Figure 3 . In addition to commonly used USB to RS-232 serial conversion , FT2232C also can be converted into other interfaces such as RS422, RS485 and CPU -style FIFO and so on . The specific circuit are shown in Figure 4, Figure 5 , Figure 6. For convenience, the figure is still only one channel with an example . 3 Conclusion With the USB bus technology , interface extensions and interface converter is always open to problems . Based on that , FT2232C increasingly optimistic about prospects for the application . Application FT2232C can be easily extended over RS-232 Interface , RS-422 Interface , RS-485 interface, USB interface, can also be converted to SPI bus interface . USB extension or conversion of other interfaces of the program is not only economical and practical, no expansion slot occupied by the host resources, but also simple and convenient , its features gradually appear . USB interface device now has to play a major role in many fields . I believe FT2232C applications will more and more widely .