Definition and function of isolated 485 chip

This article describes the definition and role of the isolated 485 chip.

485 chip definition with isolation

The MAX485 interface chip is an RS-485 chip from Maxim.

The MAX485, MAX487-MAX491, and MAX1487 are low-power transceivers for RS-485 and RS-422 communications, each with a driver and a receiver. The MAX483, MAX487, MAX488, and MAX489 feature a slew-rate driver that reduces EMI and reduces reflections caused by improper termination matching cables for error-free data transfer up to 250kbps. The MAX481, MAX485, MAX490, MAX491, and MAX1487 have unrestricted driver slew rates for transfer rates up to 2.5Mbps.

These transceivers draw between 120μA and 500μA at no-load or full-load conditions where the driver is disabled. In addition, the MAX481, MAX483, and MAX487 feature a low-current shutdown mode that consumes only 0.1μA. All devices operate from a single 5V supply.

It operates from a single power supply +5 V with a rated current of 300 μA and uses half-duplex communication. It performs the function of converting the TTL level to the RS-485 level. The structure and pins of the MAX485 chip are very simple and contain a driver and receiver inside. The RO and DI terminals are the output of the receiver and the input of the driver respectively. When connecting with the MCU, it only needs to be connected to the RXD and TXD of the MCU respectively; the /RE and DE terminals are the enable and receive terminals respectively, when / When RE is logic 0, the device is in the receiving state; when DE is logic 1, the device is in the transmitting state. Because MAX485 works in half-duplex state, it is only necessary to control these two pins with one pin of the single-chip microcomputer; The A terminal and the B terminal are respectively received and transmitted differential signal terminals. When the level of the A pin is higher than B, the data representing the transmission is 1; when the level of A is lower than the B terminal, the data represented by the transmission is 0. Wiring is very simple when connected to a microcontroller. Only one signal is needed to control the reception and transmission of the MAX485. At the same time, a matching resistor is added between the A and B terminals, and a 100 Ω resistor is generally selected.

With the role of isolated 485 chip

The MAX485 is a low-power transceiver for RS-485 and RS-422 communication. The MAX485's driver slew rate is unrestricted and can achieve transfer rates up to 2.5Mbps. These transceivers draw between 120μA and 500μA at no-load or full-load conditions where the driver is disabled. All devices operate from a single 5V supply. The driver has a short-circuit current limit and can place the driver output in a high-impedance state through a thermal shutdown circuit. The receiver input has a fail-safe feature that ensures a logic high output when the input is open. Has high anti-interference performance. MAX485 is the most common RS422 chip on the market, and it is also the largest RS422 chip. The cost-effective, high-quality, stable supply is the main reason why most manufacturers adopt it.