Every semiconductor company has one or two star products during its development. These products help the company gain fame and establish a solid position in the semiconductor market. In the history of Maxim Integrated, there is such a star product that helped the company achieve profitability in its first year and successfully IPO in 1988!

That’s right! It is the MAX232 that created myths and history! It was an innovative product independently developed by Maxim Integrated in 1987, which first integrated power supply and interface, directly converting RS-232 levels into TTL-compatible logic levels, triggering a revolution in serial communication!

Nearly 30 years have passed, and RS-232 serial communication is still used in computers and peripheral devices, extending to industrial equipment, POS machines, blood glucose meters, barcode scanners, automotive data communication, and other low-cost, low-speed communication systems. Even today, the MAX232 is still in use. It is not an exaggeration to say that in the history of semiconductors, the MAX232 may be the chip with the longest lifespan. Today, we will unveil the big data behind this star product.

If you are not familiar, please take a look at the back of your desktop computer, there must be this interface, highlighted in yellow.

The full name of the RS-232C standard (protocol) is EIA-RS-232C standard, where EIA (Electronic Industry Association) represents the American Electronic Industry Association, RS (recommended standard) represents the recommended standard, 232 is the identification number, and C represents the latest modification of RS232 (1969). Prior to this, there were RS232B and RS232A. It specifies the connection cable, mechanical, electrical characteristics, signal functions, and transmission processes. Common physical standards include EIA RS-422A, EIA RS-423A, and EIA RS-485. Here we only introduce EIA RS-232C (referred to as 232, RS232). For example, the COM1 and COM2 interfaces on IBM PC machines are RS-232C interfaces, which are the parts highlighted in yellow.

EIA-RS-232C specifies the electrical characteristics, logic levels, and various signal line functions.

On TxD and RxD:

Logic 1 (MARK) = -3V to -15V

Logic 0 (SPACE) = +3V to +15V

On control lines such as RTS, CTS, DSR, DTR, and DCD:

Signal valid (on, ON state, positive voltage) = +3V to +15V

Signal invalid (off, OFF state, negative voltage) = -3V to -15V

The RS-232 protocol was initially intended for PC communication. The RS-232 serial port was first used in IBM personal computers and other early desktop computers, then expanded to computer peripherals such as printers and modems, and further extended to the embedded field. Because RS-232 does not require any licensing fees and is low-speed, stable, and reliable, “despite new digital interface standards still being developed, the unassuming RS-232 serial port remains a very popular data transmission method. It is powerful and easy to use, and for those demanding digital interfaces, the RS-232 interface remains an attractive backup,” as described on Maxim’s official website.

Today, the RS-232 protocol is still widely used in embedded electronic products, industrial control systems, network devices, and scientific instruments. In the embedded field, especially in the microcontroller domain, RS-232 protocol is often needed. When microcontrollers communicate with PCs via serial ports, although microcontrollers have serial communication capabilities, the signal levels provided by microcontrollers do not match the RS232 standard. Therefore, level conversion is required through chips like MAX232. The difference between UART in microcontrollers and RS232 in computers lies in the voltage levels; the computer serial port uses RS232 levels, while the microcontroller UART uses TTL levels. If level conversion is not performed, microcontrollers cannot communicate directly with computer serial ports. As long as the voltage levels are unified, both can communicate directly. This is where chips like MAX232 come into play, as MAX232 does not modify the data being communicated between the two, it only unifies the voltage levels, ensuring there are no communication barriers. Therefore, from this perspective, MAX232 should have a long lifecycle ahead.

In some open-source communities like Raspberry Pi and Arduino, many makers are also using MAX232 for serial communication.

Even today, the MAX232 is still available for sale on Maxim’s online store, and the price is quite reasonable. (Open your browser and enter the link to view details in Maxim’s online store: https://www.maximintegrated.com/cn/storefront/storefront.html )

The MAX232 chip operates on a single +5V power supply and requires only a few external capacitors to complete the conversion from TTL to RS232 levels, with two channels. Pins 13 (R1IN), 12 (R1OUT), 11 (T1IN), and 14 (T1OUT) form the first data channel. Pins 8 (R2IN), 9 (R2OUT), 10 (T2IN), and 7 (T2OUT) form the second data channel. TTL/CMOS data from T1IN and T2IN is converted to RS-232 data sent to the computer’s DP9 connector; RS-232 data from the DP9 connector is converted to TTL/CMOS data from R1OUT and R2OUT.

Typical configuration diagram of MAX232

1. Strong product definition— MAX232 specifically targets the working range of RS-232 positive and negative 15V levels for conversion. Some chips either have too narrow or too wide conversion levels, which are not the most suitable. Therefore, when designing a product, the most suitable and targeted chip, though seemingly niche, often has a large market.

2. Simple and easy to use— Why do engineers in the embedded field prefer RS-232? Because this protocol is simple, yet it can handle the complex requirements of many electronic subsystems, allowing data to be transmitted as simply as possible through serial communication. This simplicity reflects human nature, and MAX232 is very easy to use. Therefore, when designing, one must consider how to simplify the designer’s application.

3. Analog-to-digital and digital-to-analog conversion signal chips will always have vitality— Our human body is an analog system, and various digital chips have exceptionally strong digital processing capabilities. Therefore, the demand for chips related to analog-to-digital or digital-to-analog conversion will always exist. With the development of technology, new high-speed digital communication protocols are constantly emerging, which will certainly involve the need for analog-digital conversion, harboring enormous business opportunities.

Now, emerging applications such as wearables, VE/AR, autonomous driving, industrial automation, smart homes, and the Internet of Things are continuously emerging. Maxim is actively participating, and perhaps in the near future, you will see another star product from Maxim. We are always striving to serve the semiconductor industry!