UM232R 查看數據表（PDF） - Future Technology
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UM232R Datasheet PDF : 19 Pages
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6.2 Self Powered Configuration
Vcc = 3.3V – 5V
MCU
TXD
RXD
RTS#
CTS#
TXD 1
J1
RTS# 3
RXD 5
GND 7
CTS# 10
J2
12
Page 14
Vcc = 3.3V – 5V
24 GND
21 VCC
20 RST#
17 PU1
16 PU2
15 VCC
14 USB
13
Figure 5 - Self Powered Configuration
Figure 5 illustrates the UM232R 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 5 illustrates a self powered design
which has a 3.3V - 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 powered devices are as follows –
i) A Self Powered device should 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. In this case
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 FT232R 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 FT232R is in reset, the UART interface 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 5 is also an example of interfacing the FT232R to a Microcontroller (MCU) UART interface. This example uses
TXD and RXD for transmission and reception of data, and RTS# / CTS# hardware handshaking.
Optionally, RI# can be connected to another I/O pin on the MCU and could be used to wake up the USB host
controller from suspend mode. One of the CBUS pins could be configured as a 6/12/24/48 MHz clock output which
can be used to clock the MCU. If the MCU is handling power management functions, then a CBUS pin can be
configured as PWREN# and should also be connected to an I/O pin of the MCU.
UM232R USB-Serial UART Development Module Datasheet Version 1.02
© Future Technology Devices International Ltd. 2005
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