FT232RL-REEL Datasheet, PDF (30/47 Pages) Future Technology Devices International Ltd. – USB UART IC

7.3 USB to RS422 Converter
Vcc
5
SHIELD
Ferrite Bead
1
2
3
4
10nF +
GND
100nF
Vcc
4.7uF +
GND
100nF
VCC
USBDM
USBDP
TXD
RXD
RTS#
CTS#
VCCIO
FT232R
NC
RESET#
NC
OSCI
OSCO
DTR#
DSR#
DCD#
RI#
CBUS0
CBUS1
3V3OUT
CBUS2
A
T CBUS3
G G G G E ^PWREN#
N N N N S CBUS4-
D D D D T SLEEP#
GND
Vcc
GND
10K
FT232R USB UART IC Datasheet
Version 2.13
Document No.: FT_000053 Clearance No.: FTDI# 38
Vcc
RS422 LEVEL
4 ^CONVERTER
10
5
9
3
11
2
12
SP491
6
7
Vcc
RS422 LEVEL
CONVERTER
4
10
5
9
3
11
2
12
SP491
6
7
120R
120R
TXDM
TXDP
RXDP
RXDM
RTSM
RTSP
CTSP
GND
TXDM
TXDP
RXDP
RXDM
RTSM
RTSP
CTSP
CTSM
SHIELD
DB9M
CTSM
Figure 7.3 USB to RS422 Converter Configuration
An example of using the FT232R as a USB to RS422 converter is shown in Figure 7.3. In this application,
two TTL to RS422 Level Converter ICs are used on the serial UART interface of the FT232R to convert the
TTL levels of the FT232R to RS422 levels. There are many suitable level converter devices available. This
example uses Sipex SP491 devices which have enables on both the transmitter and receiver. Since the
SP491 transmitter enable is active high, it is connected to a CBUS pin in SLEEP# configuration. Th e
SP491 receiver enable is active low and is therefore connected to a CBUS pin PWREN# configuration. This
ensures that when both the SP491 transmitters and receivers are enabled then the device is active, and
when the device is in USB suspend mode, the SP491 transmitters and receivers are disabled. If a similar
application is used, but 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
standby current of 2.5mA is met.
The SP491 is specified to transmit and receive data at a rate of up to 5 Mbaud. In this example the
maximum data rate is limited to 3 Mbaud by the FT232R.
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