Adafruit RS232 Full Breakout with DE9-M

If you want to interface with telco, retro, or industrial equipment, you’ll probably run into RS-232 interfaces. The Adafruit RS232 Full-Pinout Breakout with 8 Channels of UART to RS-232 Level Shifters is your friend in such cases. It gives you 5 input and 3 output channels of level shifting and takes care of the high/negative voltage generation all in a low-cost breakout board. We use the trusty MAX3243 from TI, a classic chip part of the MAX232 lineage, so you know it will work great for all your RS-232 needs, up to 250Kbps.

We also stock the DE-9 Female version.

RS-232 is what we had before USB: a 9- or 25-pin D-Sub connector that allowed data plus flow control lines. Many folks may remember these interfaces were used for mice, modems, barcode scanners, teletypes, and more. We still find devices sold with RS-232 ports, although many folks use a USB to RS-232 adapter these days.

This version has a DE9-M ‘male’ pin connector soldered in, take a look at the pictures to make sure this matches the device or cable you want to connect to!

If you want to use a microcontroller or microcomputer to chat with an RS-232, then thankfully, all you need is a serial port / UART (something just about any microcontroller has) and a level shifter. The level shifter is required because while most UARTs are 0-3.3V or 0-5V logic level, RS-232 requires +-6 to +-10V, yep the signal voltage goes negative! That means a specialized shifter is required to generate extra high and low voltages and safely convert the logic levels.

Sure you could buy a raw MAX232 chip and wire up the necessary capacitors, but this board does it all for you and even comes with a DE-9 connector for plugging in directly into your ‘client’ device. It can run on 3.3V power and logic, which many older chips can’t do. It also can do all 8 data pins, so you can use all of the flow control signals like RTS, CTS, DTR, DSR, DCD and RI.

We also include two separate lines from the MAX3243: ‘Valid’ and ‘Off’. The Valid line output will have logic level high when the chip detects signal voltages from the device it’s plugged into. So you can use it as a ‘connection made’ signal. There’s also the Off pin, which when set to logic high by the microcontroller will tri-state all the pins for power reduction.

This breakout comes fully assembled with a UART side for low-voltage power/logic level, and a DE-9M RS-232 side for high-voltage signals. We also include some headers so you can solder to a breadboard in a few minutes.

Specifications

• MAX3423 Features
  • Operates With 3-V to 5.5-V VCC Supply
  • Single-Chip and Single-Supply Interface for IBM™ PC/AT™ Serial Port
  • RS-232 Bus-Pin ESD Protection of ±15 kV Using Human-Body Model (HBM)
  • Meets or Exceeds the Requirements of TIA/EIA-232-F and ITU V.28 Standards
  • Three Drivers and Five Receivers
  • Operates Up To 250 kbit/s
  • Low Active Current: 300 μA Typical
  • Low Standby Current: 1 μA Typical
  • Accepts 5-V Logic Input With 3.3-V Supply
  • Serial-Mouse Driveability
• Product Dimensions: 33.7mm x 31.8mm x 14.2mm
• Product Weight: 11.0g

Resources

• Primary Guide: Adafruit RS-232 Full Pinout Level-Shifter Breakout