ft232b is a usb to serial uart with the following advanced interface features: microcontroller usb to asynchronous serial data transfer full handshake and modem interface signaling UART I/F supports 7/8 bit data, 1/2 stop bit and odd/even/mark /space/no data rate 300 => 3M baud (TTL) data rate 300 => 1M baud ( RS232 ) data rate 300 => 3M baud (RS422/RS485) 384 bytes receive buffer / 128 bytes high Transmit buffer adjustable for data throughput RX buffer timeout Fully assisted hardware or x-on/x-off handshake Built-in event support for character and line feed conditions Single supply operation to 5.25V Supports high power USB bus powered devices via pwren pin uart based and integrated 3.3V regulator with 5V and 3.3V logic for USB IO Integrated power-on reset circuit Integrated 6MHz–48MHz clock multiplier PLL uhci/ohci/ehci host controller compatible Compatible with USB 1.1 and USB 2.0 USB video, PID, serial number and description string in product external EEPROM 32-LD LQFP package ( FT232B L) or 32-LD QFN package (FT232BQ).

1 Typical applications USB to RS232/RS422/RS485 converters Upgrade old peripherals to USB cellular and cordless phones USB data transfer cables and interfaces mcu/pld/fpga based design with universal serial bus USB audio and low bandwidth video data transfer pda Data transfer to usb USB Industrial Control USB MP3 Player Interface Set Top Box PC-USB Interface USB Hardware Modem 98, 98SE, ME, 2000, Server 2003, XP and Server 2008 Windows 7 32, 64-bit Windows XP and XP 64-bit Windows Vista and Vista 64-bit Embedded OS Windows CE 4.2, 5.0 and 6.0 Mac OS 8/9, OS-XLinux 2.4 and above Royalty Free D2XX Direct Driver (USB Driver + DLL S/W Interface) Windows 98, 98SE, ME, 2000, Server 2003, XP and Server 2008 Windows 7 32, 64-bit Windows XP and XP 64-bit Windows Vista and Vista 64-bit Embedded OS Windows CE 4.2, 5.0 and 6.0 Linux 2.4 and higher

Figure illustrates a typical USB self-powered configuration. USB self-powered devices get power and do not draw current from the USB bus. The basic rules of the usb itself are as follows: a) When the USB host or hub controller is powered down. b) A self-powered device can receive as much current as it can during normal operation and USB suspend because it has its own power source. c) Self-powered devices can be used with any USB host as well as bus and self-powered USB hubs Pull pwrctl (pin 14) high to configure the device using the USB bus power descriptor. The descriptors in the power EEPROM should be programmed to zero. The USB power descriptor option in the EEPROM should be programmed to zero (self powered). To meet the requirement, the 1.5K pull-up resistor on USBDP is connected to RSTOUT as per the bus power circuit. However, the USB bus power is used to control the reset pin of the FT232B device. When the USB host or hub is powered, rstout will pull the 1.5K resistor on USBDP to 3.3V, thus identifying the device as a USB full speed device. When the USB host or hub is powered off, the reset will be too low and the device will remain in reset. Since reset is low, RSTOUT will also be low, so no current will force the USBDP off via the 1.5K pull-up resistor when the host or hub is powered down. Failure to do so may cause some USB host or hub controllers to power up erratically. Note: When the FT232B is reset, the UART interface pins are all in tri-state. These pins have internal 200K pull-up resistors to VCCIO, so they will pull gently high unless driven by some external logic.

The figure shows how to configure the FT232B to interface with a 3.3V logic device. In this example, a discrete 3.3V regulator is used to provide 3.3V logic from the USB power supply. VCCIO is connected to the output of the 3.3V regulator, which will cause the UART interface IO pins to drive levels at 3.3V. For USB bus powered circuits, there are a few factors that must be considered when choosing a regulator: a) The regulator must be able to maintain its output voltage at an input voltage of 4.35 volts. A low dropout (LDO) regulator must be selected. b) The quiescent current of the regulator must be low to meet the current requirement <= 500uA during total USB suspend during USB suspend. An example of a family of regulators that meet these requirements is the Microchip MCP1700 series. These devices can deliver up to 250mA with a quiescent current of less than 1mA. In some cases, if only a small amount of current (<5mA) is required, the FT232B's built-in regulator can be used to supply 3.3V without requiring any other parts. In this case, connect VCCIO to the 3V3OUT pin of the FT232B. Note: It should be emphasized that in a bus powered design, the 3.3V supply for VCCIO with 3.3V logic interface should come from the LDO provided by the USB bus, or from the ft232b, not from any other source.

Diagram illustrating how to use the FT232B with a 3-pin ceramic resonator. Suitable parts are ceramic resonators from Murata's Ceralock series or equivalent. 3-pin ceramic resonators have load capacitors built into the resonator, so no external load capacitors are required. This makes economical allocation. This Murata ceramic resonator has an accuracy of ±0.1% and is especially designed for USB full-speed applications. A 1 megohm load resistor between XTIN and XTOUT is recommended to guarantee this accuracy. Diagram illustrating how to use the FT232B with a 6MHz crystal or a 2-pin ceramic resonator. These devices do not have built-in load capacitors. Display must be added between xtin, xtout and gnd. The capacitor in the example shows a value of 27pF, which is good for many crystals and some resonators, but in any case the value is chosen based on the manufacturer's recommendations. If using a crystal, use the parallel cut type. If using a resonator, see the previous note Frequency Accuracy.

The diagram illustrates how to connect the FT232B to a 93C46 (93C56 or 93C66) EEPROM. EECS (pin 32) is connected directly to the chip select (CS) pin of the EEPROM. EESK (pin 1) is directly connected to the clock (SK) pin of the EEPROM. eData (pin 2) is directly connected to the electrically erasable programmable read-only memory. The data output (DOUT) of the EEPROM may be driven out as the eData pin of the FT232B. To prevent possible data conflicts in this case, DOUT of the EEPROM is connected to EEDATA of the FT232B through a 2.2K resistor. After a power-on reset or USB reset, the FT232B will scan the EEPROM to determine (a) if the EEPROM is connected to the device and (b) if the data in the device is valid. If both conditions are true, then ft232b will use the data from the eeprom, otherwise it will use its built-in defaults. When a valid command is issued to the eeprom from the ft232b, the eeprom will pull the pin down by pulling it down. To check this, it is necessary to pull Dout up the resistor with a 10km pull. If the command ack does not happen, then eData will be pulled high by the 10K resistor During this part of the loop, the device will detect an invalid command or the absence of eeprom. These eeproms come from two different sources such as microchip, stmicro, issi, etc. One is configured to be 16 bits wide and the other is configured to be 8 bits wide.

The FT232B requires an EEPROM with a 16-bit wide configuration, like the Microchip 93LC46B device. The EEPROM must be able to read data at a 1MB clock rate from a supply voltage of 4.35V to 5.25V. Most of the available parts can do this. Check the manufacturer's datasheet for how to connect pins 6 and 7 of the EEPROM. Some devices specify it as "no connection", others use it to select 8/16-bit mode or test functionality. Some of the other parts have the pins turned out 90 degrees. It is recommended to select the required parts and their careful selection. The eeprom can be "shared" between the ft232b and another external device such as a mcu. However, this can only be done when the FT232B is in reset, as it tri-states the EEPROM interface at the time. A typical configuration will use four bits of one MCU IO port. A little bit will work for keeping the FT232B in reset (using reset) when powered on, the other three will be connected to the EEC, the eesk and eedata pins of the ft232b to read/write data to the eeprom at this point. Once the MCU has read/written the EEPROM, it needs to be reset high to allow the FT232B to configure itself and pass USB.

The FT232B has two IO pins for controlling LED status indicators, one for transmitting data and the other for receiving data. When data is being sent/received, the individual pins are driven low from tri-state to provide an indication on the data transfer LED. Use a digital one-time timer so that even a small portion of the data transfer is visible to the end user. The diagram shows a configuration using two separate LEDs - one for transmitting data and one for receiving data. In the picture, the transmit and receive LEDs are connected together to form a single LED indicating any activity of sending or receiving data. Another possibility (not shown here) is to use a graph based on having a separate LED that can be compared based on transmit activity versus receive activity. Note that the LED is connected to VCCIO.