FT232R Future Technology Devices Intl Ltd., FT232R Datasheet - Page 24

• Manufacturer Part Number: FT232R
• Manufacturer: Future Technology Devices Intl Ltd.

Figure 15 -Example USB to RS422 Converter Configuration
Figure 15 illustrates how to connect the UART interface of the FT232R to a TTL – RS422 Level Converter I.C. to
make a USB to RS422 converter. There are many such level converter devices available – this example uses Sipex
SP491 devices which have enables on both the transmitter and receiver. Because the transmitter enable is active
high, it is connected to a CBUS pin in SLEEP# configuration. The receiver enable is active low and so is connected
to a CBUS pin PWREN# configuration. This ensures that both the transmitters and receivers are enabled when the
device is active, and disabled when the device is in USB suspend mode. If the design is USB BUS powered, it may be
necessary to use a P-Channel logic level MOSFET (controlled by PWREN#) in the VCC line of the SP491 devices to
ensure that the USB stand-by current of 500μA is met.
The SP491 is good for sending and receiving data at a rate of up to 5 Megbaud – in this case the maximum rate is
limited to 3 Megabaud by the FT232R.
FT232R USB UART I.C. Datasheet Version 1.02
SHIELD
5
8.3 USB to RS422 Converter Configuration
1
2
3
4
10nF
100nF
+
Ferrite
Bead
4.7uF
+
Vcc
Vcc
100nF
VCC
USBDM
USBDP
VCCIO
RESET#
OSCI
OSCO
3V3OUT
NC
NC
A
G
N
D
FT232R
G
N
D
G
N
D
G
N
D
T
E
S
T
PWREN#
CBUS4 -
CBUS2
CBUS3 -
SLEEP#
CBUS0
CBUS1
DSR#
DCD#
RTS#
CTS#
DTR#
RXD
TXD
RI#
© Future Technology Devices International Ltd. 2005
4
5
2
4
5
2
3
3
RS422 LEVEL
RS422 LEVEL
CONVERTER
CONVERTER
Vcc
6
Vcc
6
SP491
SP491
7
7
10
10
9
11
12
9
11
12
120R
120R
TXDM
TXDP
RXDP
RXDM
RTSM
RTSP
CTSP
CTSM
RXDM
TXDM
RXDP
RTSM
CTSM
TXDP
RTSP
CTSP
GND
SHIELD
DB9M