USB to MCU UART Interface

Figure -Example USB to MCU UART Interface
Figure is an example of interfacing the FT232R to a Microcontroller (MCU) UART interface. This example uses TXD and RXD for transmission and reception of data, and RTS# / CTS# hardware handshaking. Also in this example CBUS0 has been configured as a 12MHz output which is being used to clock the MCU.
Optionally, RI# can be connected to another I/O pin on the MCU and could be used to wake up the USB host controller from suspend mode. If the MCU is handling power management functions, then a CBUS pin can be configured as PWREN# and should also be connected to an I/O pin of the MCU.

USB to RS232 Converter Configuration

Figure 15 - Example USB to RS232 Converter ConfiguratiUSB to RS232 on
Figure 15 illustrates how to connect an FT232R as a USB to RS232 converter. A TTL – RS232 Level Converter I.C. is used on the serial UART of the FT232R to make the RS232 level conversion. This, for example can be done 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.
An example of a device which can be used for this is a Sipex SP213EHCA which is capable of RS232 communication at up to 500kΩ baud. If a lower baud rate is acceptable, then several pin compatible alternatives are available such as the Sipex SP213ECA , the Maxim MAX213CAI and the Analog Devices ADM213E, which are all 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 it to PWREN# instead of SLEEP#.
In the above example CBUS0 and CBUS1 have been configured as TXLED# and RXLED#, and are being used to drive two LEDs.

USB to RS422 Converter Configuration

Figure -Example USB to RS422 Converter Configuration
Figure illustrates how to connect the UART interface of the FT232R to a TTL – RS422 Level Converter I.C. to make a USB to RS422 converter. There are many such level converter devices available – this example uses Sipex SP491 devices which have enables on both the transmitter and receiver. Because the transmitter enable is active high, it is connected to a CBUS pin in SLEEP# configuration. The receiver enable is active low and so is connected to a CBUS pin PWREN# configuration. This ensures that both the transmitters and receivers are enabled when the device is active, and disabled when the device is in USB suspend mode. If the design is USB BUS powered, it may be necessary to use a P-Channel logic level MOSFET (controlled by PWREN#) in the VCC line of the SP491 devices to ensure that the USB stand-by current of 500μA is met.
The SP491 is good for sending and receiving data at a rate of up to 5 Megbaud – in this case the maximum rate is limited to 3 Megabaud by the FT232R.

USB to RS485 Converter Configuration

Figure - Example USB to RS485 Converter ConfigurationFigure illustrates how to connect the FT232R’s UART interface to a TTL – RS485 Level Converter I.C. to make a USB to RS485 converter. This example uses the Sipex SP481 device but there are similar parts available from Maxim and Analog Devices amongst others. The SP481 is a RS485 device in a compact 8 pin SOP package. It has separate enables on both the transmitter and receiver. With RS485, the transmitter is only enabled when a character is being transmitted from the UART. The TXDEN signal CBUS pin option on the FT232R is provided for exactly this purpose and so the transmitter enable is wired to CBUS2 which has been configured as TXDEN. Similarly, CBUS3 has been configured as PWREN#. This signal is used to control the SP481’s receiver enable. The receiver enable is active low, so it is wired to the PWREN# pin to disable the receiver when in USB suspend mode. CBUS2 = TXDEN and CBUS3 = PWREN# are the default device configurations of these pins.
RS485 is a multi-drop network – i.e. many devices can communicate with each other over a single two wire cable connection. The RS485 cable requires to be terminated at each end of the cable. A link is provided to allow the cable to be terminated if the device is physically positioned at either end of the cable.
In this example the data transmitted by the FT232R is also received by the device that is transmitting. This is a common feature of RS485 and requires the application software to remove the transmitted data from the received data stream. With the FT232R it is possible to do this entirely in hardware – simply modify the schematic so that RXD of the FT232R is the logical OR of the SP481 receiver output with TXDEN using an HC32 or similar logic gate.