This is a protocol translator circuit. This circuit uses the MAX3162, it contains both RS-485 and RS-232 transmitters and receivers. This IC contains wide range of communication devices, that can convert bidirectionally between RS-485 and RS-232 signals. Here is the circuit :
The upper circuit is the translator for point to point application, and the lower is for multipoint application. The RTS signal, R1IN, is used to controls the translation’s direction. It will translate a differential RS-485 receiver-input signal into a single-ended RS-232 transmitter output. And also, it will translate the single-ended RS-232 receiver-input signal into a differential RS-485 transmitter output. It controls the RS-485 transceiver acts as a receiver or a transmitter. The system monitors the RS-485 driver input, DI, to make sure that a byte of data in the UART’s transmit buffer has been transmitted. So before using the DE input to change the bus direction, the system must either actively monitor the DI input or allow a fixed time delay. Other direction-control techniques are driving the DE input with data while pulling the A-B lines apart (connecting a pull-down resistor from B to ground and a pull-up resistor from A to 5V) and using a microcontroller. Resistor’s value is typically 1kO. [Circuit's schematic diagram source: maxim-ic.com]
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