Datasheet

Document No.: FT_000053

FT232R USB UART IC Datasheet Version 2.02

Clearance No.: FTDI# 38

7.3 USB to RS422 Converter

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. The

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.