Serial port, RS232/422/485, DE-9M or screw terminal?

Putting a kit together and I'm humming & hawing over the serial port.

Build options would be a
DE-9M with MAX3160 (RS232, 422 or 485 jumper selectable)
Screw terminals to MAX232 or DS485 IC (RS232 or 485 drop in DIP IC to select)

It's for an embedded device like the OCELOT or Elk-Magic.

Comments & questions welcome.

Comments & questions welcome.

Now we're talking...

Thanks for using DE-9 (because that's what it IS). :slight_smile:
I rage internally whenever someone uses DB9: "Oh, DB9? Really? Well, hey, you know what?..."
(Everyone, FWIW, that same size shell with 15 pins in it, like a VGA connector, is a DE-15.)


Correct about DE, it’s become standard to refer to all D-sub connectors as DB unfortunately, probably the fault of the early IBM PCs. If you look at the MAX3160 example schematic even they use “DB9” connectors :slight_smile:

I like both methods, the MAX3160 is an expensive chip though, does that matter?

If you use screw terminals I’d use the plug/socket types as requiring a screwdriver to remove/replace wires is annoying and error prone.

If you use a D-sub connector people may have to solder up a cable, that’s a pain as well.

Another option is to just use a 2x5 way header and use an IDC DB9 DE9 connector. This also allows a neat way to mount the connector on a panel or enclosure side.


:slight_smile: Yes DE-9, never understood how DB (25pin) got the nod.

The 2x5 header might be a good option with screw terminals, It would need five terminals to support RS232, 422 & 485. Hmm.

The MAX3160 evaluation board uses a DE-9 and the site uses terminals (and lots of jumpers) on their conversion kits. As for the cost the MAX3160 does offer a lot of flexibility for a preassembled board. I've already started the initial schematics, I'll post another thread describing the project ASAP in this sub-forum.

five terminals to support RS232, 422 & 485.

I don't know what this is for (no idea what OCELOT and Elk-Magic are) but adding another terminal will allow a power supply to be run down the cable as well.


It’s not a shield but a small PCB with two 28pin sockets a 26pin header and a 10pin I2C connector. Required 5V regulated @ 1A.

It’s for a daisy chain-able 4 Relay (with snubber option), 4 Opto input, RS232-485 & XBee board that supports the ATmega328P, PIC18F26J11 or Raspberry Pi. Optional 3.3V USB header will allow it to be used like an Arduino.

Options might include pads for a DS3231 accurate RTCC and an I2C EEPROM, possibly 433MHz RF receiver support.

Still on the fence about going with the DE-9M and looking at the ISL3330 as a inexpensive replacement for the the MAX3160.

A six screw terminal block, 5V,TX,RX,CTS,RTS,GND seems tempting since with the ISL3330 you have to jumper the RS422 outputs to the inputs to put it in RS485 mode. (the MAX3160 does not).

Another thought might be to use a RJ-45 (ethernet/cat-5/cat-6) jack which gives you 8 wires. You can find raw terminals that you would wire at home improvement centers (Home Depot or Lowes in the USA) as well as places like Radio Shack. For a little more money, you can get RJ-45 breakout boards that gives you 8 pins in a breadboard/protoboard friendly layout or screw terminals, depending on your needs.