What is causing my serial RS232 cable problems?

Here are some options, but we definitely recommend you contact our Support team.

Connecting pin one (earth ground) at both ends:
This creates a giant antenna, earth ground should only be connected at one end and generally at the device that is most grounded.

Using CAT5 cabling:

While CAT5 cable might work for a short while for RS232 communications, it is not designed for that application. CAT5 cable is twisted pair cabling for ethernet. Because it is designed for lower voltages and data that is checked packet-by-packet, CAT5 ethernet cable used for serial purposes can potentially cause a scrapped part by dropping data, short out the machine because of improper voltages and signals, and even crash a machine by sending bad data or omitting it. CAT5 cable is never recommended for RS232 communications. We recommend Predator Grizzly cable for RS232 serial communication because it is designed for this exact purpose and will prevent loss of data and interference issues.

Cable is not properly jumpered at CNC end:
Most CNCs will require jumpering of some sort. Most common is for pins 4 & 5 plus pins 6, 8 & 20.

Using unshielded cable:
Unshielded cable should never be used in a machine shop environment.

Twisted pair cabling not properly balanced:
If you use twisted pair, pins 2 and 3 can not be on the same pair. It is also recommended that you ground the other half of the pair for pins 2 and 3.

Cable with too few wires:
Most CNCs will only need TD, RD and SG, but some will require hardware handshaking and thus require more wires.

Improper positioning of cable:
Do not strap RS232 cabling to electrical conduit in the shop.

Incorrectly pinning out a DB9 to DB25 cable or adapter:
See the chart above, note that pins 2 & 3 are opposite from DB9 to DB25.

Category: RS232 Serial Cable