RS-232 (formerly known as V.24) is a well-established standard for serial interfaces. Although it primarily defines voltage levels and maximum cable lengths, RS-232 is widely used for asynchronous communication with start and stop bits. Whether you’re in the computer, IoT, or vending machine industry, you’ve likely encountered RS-232.

Is MDB a Form of RS-232?

No, MDB (Multi Drop Bus) is not a form of RS-232. If you want to know what MDB exactly is, click on this link!

Why Can’t RS-232 Communicate Directly with MDB?

RS-232 is a point-to-point connection method that uses voltage levels of +3V to +15V and -3V to -15V to transmit data. In contrast, MDB is a one-to-many connection method that uses TTL logic levels of 5V and 0V. It is based on current flow, such as short-circuiting a 5V source or driving an optocoupler with 5V. This fundamental difference in voltage levels and connection methods makes direct communication between RS-232 and MDB impossible.

Can “Physical Translation” Connect RS-232 to MDB?

MDB uses a 9600 baud rate, which is also common in RS-232, giving an initial impression of compatibility. However, significant challenges remain:

1. Data Bits: RS-232 typically transmits 8-bit data (bytes), sometimes using 7 bits with an added parity bit. MDB, however, uses a 9th data bit, resulting in 9-bit transmissions per byte. Standard serial ports on PCs do not support 9-bit transmissions, creating a compatibility issue.
2. Stringent Timing Requirements: MDB demands precise timing. Peripherals must respond almost instantly to facilitate communication with multiple devices on the bus. Modern operating systems struggle to meet these stringent timing requirements, complicating direct interfacing.