Figure -Example USB to RS422 Converter Configuration
Figure 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.
Figure 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.
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