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2. Features and Enhancements
2.1 Key Features
This section summarises the key features and enhancements of the FT232RL IC device which is used on the
EVAL232R Module. For further details, consult the FT232R datasheet, which is available from the FTDI website.
Integrated Clock Circuit - Previous generations of FTDI’s USB UART devices required an external crystal or ceramic
resonator. The clock circuit has now been integrated onto the device meaning that no crystal or ceramic resonator is
required. However, if required, an external 12MHz crystal can be used as the clock source.
Integrated EEPROM - Previous generations of FTDI’s USB UART devices required an external EEPROM if the
device were to use USB Vendor ID (VID), Product ID (PID), serial number and product description strings other than
the default values in the device itself. This external EEPROM has now been integrated onto the FT232R chip meaning
that all designs have the option to change the product description strings. A user area of the internal EEPROM is
available for storing additional data. The internal EEPROM is programmable in circuit, over USB without any additional
voltage requirement.
Preprogrammed EEPROM - The FT232R is supplied with its internal EEPROM preprogrammed with a serial number
which is unique to each individual device. This, in most cases, will remove the need to program the device EEPROM.
Integrated USB Resistors - Previous generations of FTDI’s USB UART devices required two external series resistors
on the USBDP and USBDM lines, and a 1.5 kΩ pull up resistor on USBDP. These three resistors have now been
integrated onto the device.
Integrated AVCC Filtering - Previous generations of FTDI’s USB UART devices had a separate AVCC pin - the
supply to the internal PLL. This pin required an external R-C filter. The separate AVCC pin is now connected internally
to VCC, and the filter has now been integrated onto the chip.
Less External Components - Integration of the crystal, EEPROM, USB resistors, and AVCC filter will substantially
reduce the bill of materials cost for USB interface designs using the FT232R compared to its FT232BM predecessor.
Configurable CBUS I/O Pin Options - There are now 5 configurable Control Bus (CBUS) lines. Options are TXDEN
- transmit enable for RS485 designs, PWREN# - Power control for high power, bus powered designs, TXLED# - for
pulsing an LED upon transmission of data, RXLED# - for pulsing an LED upon receiving data, TX&RXLED# - which
will pulse an LED upon transmission OR reception of data, SLEEP# - indicates that the device going into USB
suspend mode, CLK48 / CLK24 / CLK12 / CLK6 - 48MHz, 24MHz,12MHz, and 6MHz clock output signal options.
There is also the option to bring out bit bang mode read and write strobes (see below). The CBUS lines can be
configured with any one of these output options by setting bits in the internal EEPROM. The device is supplied with
the most commonly used pin definitions preprogrammed - see Section 8 for details.
Enhanced Asynchronous Bit Bang Mode with RD# and WR# Strobes - The FT232R supports FTDI’s BM chip
bit bang mode. In bit bang mode, the eight UART lines can be switched from the regular interface mode to an 8-bit
general purpose I/O port. Data packets can be sent to the device and they will be sequentially sent to the interface
at a rate controlled by an internal timer (equivalent to the baud rate prescaler). With the FT232R device this mode
has been enhanced so that the internal RD# and WR# strobes are now brought out of the device which can be used
to allow external logic to be clocked by accesses to the bit bang I/O bus. This option will be described more fully in a
separate application note.
Synchronous Bit Bang Mode - Synchronous bit bang mode differs from asynchronous bit bang mode in that the
interface pins are only read when the device is written to. Thus making it easier for the controlling program to measure
the response to an output stimulus as the data returned is synchronous to the output data. The feature was previously
seen in FTDI’s FT2232C device. This option will be described more fully in a separate application note.
CBUS Bit Bang Mode - This mode allows four of the CBUS pins to be individually configured as GPIO pins, similar
to Asynchronous bit bang mode. It is possible to use this mode while the UART interface is being used, thus providing
up to four general purpose I/O pins which are available during normal operation. An application note describing this
feature is available separately from the FTDI website.
EVAL232R FT232RL USB to RS232 Evaluation Module Datasheet Version 0.90
© Future Technology Devices International Ltd. 2005
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