- 您现在的位置：买卖IC网 > Sheet目录1251 > UM245R (FTDI, Future Technology Devices International Ltd)MOD USB PARALLEL FIFO DEV FT245R
Document Reference No.: FT_000202
UM245R USB - Parallel FIFO Development Module Datasheet Version 1.04
Clearance No.: FTDI# 124
7.2 Self Powered Configuration
Figure 7.2 Self-Powered Configuration
Figure 7.2 illustrates the UM245R in a typical USB self powered configuration. In this case the link on
jumper J2 is removed, and an external supply is connected to the module VCC pins. Figure 7.2 illustrate
a design which has a 4.0V - 5V supply.
A USB Self Powered device gets its power from its own power supply and does not draw current from the
USB bus. The basic rules for USB Self power devices are as follows:
i)
A Self Powered device must not force current down the USB bus when the USB Host or Hub
Controller is powered down.
ii) A Self Powered Device can use as much current as it likes during normal operation and USB
suspend as it has its own power supply.
iii) A Self Powered Device can be used with any USB Host and both Bus and Self Powered USB Hubs
The power descriptor in the internal EEPROM should be programmed to a value of zero (self powered).
In order to meet requirement (i) the USB Bus Power is used to control the RESET# Pin of the FT245R
device. When the USB Host or Hub is powered up the internal 1.5kΩ resistor on USBDP is pulled up to
3.3V, thus identifying the device as a full speed device to USB. When the USB Host or Hub power is off,
RESET# will go low and the device will be held in reset. As RESET# is low, the internal 1.5kΩ resistor will
not be pulled up to 3.3V, so no current will be forced down USBDP via the 1.5kΩ pull -up resistor when
the host or hub is powered down. To do this pin 14 (USB) is connected to PU2 and PU1 is connected to
RST#. Failure to do this may cause some USB host or hub controllers to power up erratically.
NOTE: When the FT245R is in reset, the FIFO interface and control pins all go tri-state. These pins have
internal 200kΩ pull -up resistors to VCCIO, so they will gently pull high unless driven by some external
logic.
Figure 7.2 also illustrates interfacing the UM245R and a Microcontroller (MCU) FIFO interface. This
example uses two MCU I/O ports: one port (8 bits) to transfer data, and the other port (4 or 5 bits) to
monitor the TXE# and RXF# status bits and generate the RD# and WR strobes to the FT245R, as
required. Using PWE# for this function is optional.
If the Remote Wakeup option is enabled in the internal EEPROM, during USB suspend mode RXF#
becomes an input which can be used to wake up the USB host controller by strobing the pin low.
? Copyright 2009 Future Technology Devices International Ltd
19
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
UMTS 2
FUSE 2A 250V TLAG IEC SMD
UPG1-4-61-303-01
MAGNETIC CIRC BRKR SP 30A TOG SW
UPL111-1-60-503
MAGNETIC CIRCUIT PROTECTOR 50A
UPL2000-D1/B
BNC PLUG CRIMP STR 7538CBL 50/PK
UPL2000-D20/B
BNC PLUG CRIMP STR 1505F 50/PK
UPL220-009
BNC PLUG FULL CRIMP STR 8218CBL
UPL220-013
BNC PLUG FULL CRIMP STR RG-59
UPL220-020
BNC PLUG FULL CRIMP STR 9248 CBL
相关代理商/技术参数
UM246
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM246M
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM247
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM247M
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM248
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM248M
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM249
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC
UM249M
制造商:未知厂家 制造商全称:未知厂家 功能描述:Analog IC