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UM245R Datasheet(PDF) 3 Page - Future Technology Devices International Ltd. |
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UM245R Datasheet(HTML) 3 Page - Future Technology Devices International Ltd. |
3 / 19 page UM245R USB-Parallel FIFO Development Module Datasheet Version 1.02 © Future Technology Devices International Ltd. 2005 Page 3 2. FT232RL Features and Enhancements 2.1 Key Features This section summarises the key features and enhancements of the FT245R IC device which is used in the UM245R Module. For further details, consult the FT245R datasheet, which is available from the FTDI website. Integrated Clock Circuit - Previous generations of FTDI’s USB to parallel FIFO interface 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 to parallel FIFO interface 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 FT245R 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 FT245R 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 to parallel FIFO interface 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 to parallel FIFO interface 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 FT245R compared to its FT245BM predecessor. Enhanced Asynchronous Bit Bang Mode with RD# and WR# Strobes - The FT245R supports FTDI’s BM chip bit bang mode. In bit bang mode, the eight parallel FIFO data bus 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 FT245R 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. Lower Supply Voltage - Previous generations of the chip required 5V supply on the VCC pin. The FT245R will work with a Vcc supply in the range 3.3V - 5V. Bus powered designs would still take their supply from the 5V on the USB bus, but for self powered designs where only 3.3V is available, and there is no 5V supply, there is no longer any need for an additional external regulator. Integrated Level Converter on FIFO Interface and Control Signals - VCCIO pin supply can be from 1.8V to 5V. Connecting the VCCIO pin to 1.8V, 2.8V, or 3.3V allows the device to directly interface to 1.8V, 2.8V or 3.3V and other logic families without the need for external level converter I.C.s 5V / 3.3V / 2.8V / 1.8V Logic Interface - The FT245R provides true CMOS Drive Outputs and TTL level Inputs. Integrated Power-On-Reset (POR) Circuit- The device incorporates an internal POR function. A RESET# pin is available in order to allow external logic to reset the FT245R where required. However, for many applications the RESET# pin can be left unconnected, or pulled up to VCCIO. |
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