通信接口ic ft2232c

 the ft2232c is a usb interface which incorporates the functionallity of two of ftdi’s second generation bm chips into a single device. a single downstream usb port is converted to two io channels which can each be individually configured as a ft232bm-style uart interface, or a ft245bm-style fifo interface, without the need to add a usb hub. there are also several new special modes which are either enabled in the external eeprom, or by using driver commands. these include synchronous bit-bang mode, a cpu-style fifo interface mode, a multi-protocol synchronous serial engine interface mode, mcu host bus emulation mode, and fast opto-isolated serial interface mode. in addition a new high drive level option means that the device uart / fifo io pins will drive out at around three times the normal power level, meaning that the bus can be shared by several devices. classic bm-style asynchronous bit-bang mode is also supported, but has been enhanced to give the user access to the device’s internal rd# and wr# strobes.

ftdi provide a royalty free virtual com port (v.c.p) driver that makes the peripheral ports look like a standard com port to the pc. most existing software applications should be able interface with the virtual com port simply by reconfiguring them to use the new ports created by the driver. using the vcp drivers an application programmer would communicate with the device in exactly the same way as they would a regular pc com port - using the windows vcomm api calls or a com port library. the ft2232c driver also incorporates the functions defined for ftdi’s d2xx drivers, allowing applications programmers to interface software directly to the device using a windows dll

• two individually configurable io channels
each of the ft2232c’s channels (a and b) can be individually configured as a ft232bm-style uart interface, or as a ft245bm-style fifo interface. in addition these channel can be configured in a number of special io modes.
• integrated power-on-reset (por) circuit
the device incorporates an internal por function. a reset# pin is available to allow external logic to reset the device where required, however for most applications this pin can simply be hardwired to vcc. a rstout# pin is provided in order to allow the new por circuit to provide a stable reset to external mcu and other devices.
• integrated rcclk circuit
used to ensure that the oscillator and clock multiplier pll frequency are stable prior to usb enumeration.
• integrated level converter on uart / fifo interface and control signals
each channel of the ft2232c has its own independent vccio pin that can be supplied by between 3v to 5v. this allows each channel’s output voltage drive level to be individually configured. thus allowing, for example 3.3v logic to be interfaced to the device without the need for external level converter i.c.’s.
• improved power management control for high-power usb bus powered devices
the pwren# pin will become active when the device is enumerated by usb, and be deactivated when the device is in usb suspend. this can be used to directly drive a transistor or p-channel mosfet in applications where power switching of external circuitry is required. the bm pull down enable feature (configured in the external eeprom) is also retained. this will make the device gently pull down on the fifo / uart io lines when the power is shut off (pwren# is high). in this mode any residual voltage on external circuitry is bled to gnd when power is removed, thus ensuring that external circuitry controlled by pwren# resets reliably when power is restored.
• support for isochronous usb transfers
whilst usb bulk transfer is usually the best choice for data transfer, the scheduling time of the data is not guaranteed. for applications where scheduling latency takes priority over data integrity such as transferring audio and low bandwidth video data, the ft2232c offers the option of usb isochronous transfer via configuration of bit in the eeprom.
• send immediate / wake up signal pin on each channel
there is a send immediate / wake up (si/wu) signal pins on each of the chips channels. these combine two functions on one pin. if usb is in suspend mode (and remote wakeup is enabled in the eeprom), strobing this pin low will cause the device to request a resume from suspend (wakeup) on the usb bus. normally, this can be used to wake up the host pc. during normal operation, if this pin is strobed low any data in the device rx buffer will be sent out over usb on the next bulk-in request from the drivers regardless of the packet size. this can be used to optimise usb transfer speed for some applications.
• low suspend current
the suspend current of the ft2232c is typically under 100 μa (excluding the 1.5k pull up resistor on usbdp) in usb suspend mode. this allows greater margin for peripherals to meet the usb suspend current limit of 500ua.
the ft2232c incorporates all of the enhancements introduced for the second generation ft232bm and ft245bm chips. these are summarised as follows :-
2.0 features and enhancements