FT232RQ R FTDI, Future Technology Devices International Ltd, FT232RQ R Datasheet - Page 28

• Manufacturer Part Number: FT232RQ R
• Description: IC USB TO SERIAL UART 32-QFN
• Manufacturer: FTDI, Future Technology Devices International Ltd
• Series: USBmadeEZ-UARTr

Specifications of FT232RQ R

• Features: USB to UART
• Number Of Channels: 1, UART
• Fifo's: 256 Byte
• Protocol: RS-232, RS-422, RS-485
• Voltage - Supply: 3.3 V ~ 5.25 V
• With Auto Flow Control: Yes
• With Modem Control: Yes
• With Cmos: Yes
• Mounting Type: Surface Mount
• Package / Case: 32-QFN
• For Use With: 768-1023 - MOD USB RS232 DEV/EVAL FT232RL768-1022 - MODULE USB - SERIAL MODULE MINI768-1021 - MODULE MINI DEVELOPMENT FT232RQ768-1019 - MODULE USB-SER UART FT232 24-DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 768-1008-2; FT232RQ R

7.2 USB to RS485 Coverter
Figure 7.2 Application Example Showing USB to RS485 Converter
An example of using the FT232R as a USB to RS485 converter is shown in Figure 7.2. In this application,
a TTL to RS485 level converter IC is used on the serial UART interface of the FT232R to convert the TTL
levels of the FT232R to RS485 levels.
This example uses the Sipex SP481 device. Equivalent devices are available from Maxim and Analogue
Devices. The SP481 is a RS485 device in a compact 8 pin SOP package. It has separate enables on both
the transmitter and receiver. With RS485, the transmitter is only enabled when a character is being
transmitted from the UART. The TXDEN signal CBUS pin option on the FT232R is provided for exactly this
purpose and so the transmitter enable is wired to CBUS2 which has been configured as TXDEN. Similarly,
CBUS3 has been configured as PWREN#. This signal is used to control the SP481‟s receiver enable. The
receiver enable is active low, so it is wired to the PWREN# pin to disable the receiver when in USB
suspend mode. CBUS2 = TXDEN and CBUS3 = PWREN# are the default device configurations of the
FT232R pins.
RS485 is a multi-drop network; so many devices can communicate with each other over a two wire cable
interface. The RS485 cable requires to be terminated at each end of the cable. A link (which provides the
120Ω termination) allows the cable to be terminated if the SP481 is physically positioned at either end of
the cable.
In this example the data transmitted by the FT232R is also present on the receive path of the SP481.This
is a common feature of RS485 and requires the application software to remove the transmitted data from
the received data stream. With the FT232R it is possible to do this entirely in hardware by modifying the
example shown in Figure 7.2 by logically OR‟ing the FT232R TXDEN and the SP481 receiver output and
connecting the output of the OR gate to the RXD of the FT232R.
Note that the TXDEN is activated 1 bit period before the start bit. TXDEN is deactivated at the same time
as the stop bit. This is not configurable.
SHIELD
5
1
2
3
4
10nF
100nF
GND
+
Ferrite Bead
Copyright © 2010 Future Technology Devices International Limited
4.7uF +
GND
Vcc
Vcc
100nF
GND
USBDM
VCCIO
RESET#
OSCI
OSCO
3V3OUT
USBDP
NC
VCC
NC
A
G
N
D
G
N
D
FT232R
G
N
D
GND
G
N
D
E
S
T
T
FT232R USB UART IC Datasheet Version 2.07
CBUS0
CBUS1
CBUS2
TXDEN
CBUS3
CBUS4
DTR#
DSR#
DCD#
RTS#
CTS#
RXD
TXD
RI#
PWREN#
RXD
TXD
3
4
2
1
RS485 LEVEL
CONVERTER
GPIO0
GPIO1
SP481
GPO
5
Vcc
VCCIO
Document No.: FT_000053
7
6
120R
10K
Link
Clearance No.: FTDI# 38
GND
SHIELD
10
DB9M
28