The RS232-C interface was developed for a single purpose. This purpose is stated by its title:

“Interface Between Data Terminal Equipment and Data Communications Equipment Employing Serial Binary Data Interchange.”

Every word in the title is significant: it describes the interface between a terminal (DTE) to a modem (DCE) for the transfer of serial data.

Short for Recommended Standard-232C, a standard interface approved by the Electronic Industries Association (EIA) for connecting serial devices. In 1987, the EIA released a new version of the standard and changed the name to EIA-232-D. And in 1991, the EIA teamed up with Telecommunications Industry Association (TIA) and issued a new version of the standard called EIA/TIA-232-E. Many people, however, still refer to the standard as RS232C or just RS232.

Almost all modems conform to the EIA-232 standard and most personal computers have an EIA-232 port for connecting a modem or other device. In addition to modems, many display screens, mice, and serial printers are designed to connect to an EIA-232 port. In EIA-232 parlance, the device that connects to the interface is called a Data Communications Equipment (DCE) and the device to which it connects (e.g., the computer) is called a Data Terminal Equipment (DTE).

The EIA-232 standard supports two types of connectors, a 25-pin D-sub type connector (DB25) and a 9-pin D-sub type connector (DB9). The type of serial communications used by PCs requires only 9 pins so either type of connector will work equally well.

Although EIA-232 is still the most common standard for serial communication, the EIA has recently defined successors to EIA-232 called RS422 and RS423. The new standards are backward compatible so that RS232 devices can connect to an RS422 port.

In the past, most IBM PC and compatible computers were typically equipped with two serial ports and one parallel port. Although these two types of ports are used for communicating with external devices, they work in different ways.

A parallel port sends and receives data eight bits at a time over 8 separate wires. This allows data to be transferred very quickly; however, the cable required is bulkier because of the number of individual wires it must contain and cable distances are generally very short.

Parallel ports are typically used to connect a PC to a printer and are rarely used for much else. A serial port sends and receives data one bit at a time over one wire. While it takes eight times as long to transfer each byte of data this way, only a few wires are required. In fact, two-way (full duplex) communication is possible with only three separate wires – one to send, one to receive, and a common signal ground wire.

The number preceding each signal name corresponds to the pin number defined in the standard.


  1.     Received Line Signal Detect (Carrier Detect)
  2.     Received Data
  3.     Transmitted Data
  4.     Data Terminal Ready
  5.     Signal Ground
  6.     Data Set Ready
  7.     Request to Send
  8.     Clear To Send
  9.     Ring Indicator


  1.     Protective Ground
  2.     Transmitted Data
  3.     Received Data
  4.     Request to Send
  5.     Clear To Send
  6.     Data Set Ready
  7.     Signal Ground
  8.     Received Line Signal Detect (Carrier Detect)
  9.     +P (for testing only)
  10.     -P (for testing only)
  11.     (unassigned)
  12.     Secondary Received Line Signal Detect
  13.     Secondary Clear To Send
  14.     Secondary Transmitted Data
  15.     Transmission signal element Timing
  16.     Secondary Received Data
  17.     Receiver Signal Element Timing
  18.     (unassigned)
  19.     Secondary Request To Send
  20.     Data Terminal Ready
  21.     Signal Quality Detector
  22.     Ring Indicator
  23.     Data Signal Rate Selector
  24.     Transmitter Signal Element Timing
  25.     (unassigned)

Sure, but it may not be worth the effort in research, soldering, testing, and cost of parts.

Normal serial cable is sensitive to interference and signal loss. We carefully engineered, manufactured and tested Grizzly cable to fit the needs of a shop floor environment.

Furthermore, your time is valuable and you have better things to do! Why not consult with experts?

No, a Grizzly cable is far different than commercial Ethernet cabling.

A CAT-5 cable is typically un-shielded, provides a balanced signal, and uses different wiring intended for a computer, as opposed to a CNC control.

The Grizzly Cable is shielded, with an ultra-low capacitance, uses unbalanced signals, and is wired for RS232 signals to be sent to and from CNC machines.

CAT-5 cables are unreliable, able to pick up RF noise very easily and have limitations regarding baud rate when running beyond RS232 specifications.

First, each wire is individually shielded with a polypropylene jacket. Second, an aluminum foil wraps around all of the pairs. Third, a metal braid shield is wrapped around the foil. Finally, a thick but flexible PVC jacket is wrapped around the metal braid.

The quality and strength of the shielding included with Predator Grizzly cables protect your data from RF noise and electrical interference. We highly recommend that you do not attempt to make your own Grizzly Cable.

In the early 1960’s, a standards committee, today known as the Electronic Industries Association, developed a common interface standard for data communications equipment. At that time, data communications were thought to mean digital data exchange between a centrally located mainframe computer and a remote computer terminal, or possibly between two terminals without a computer involved.

These devices were linked by telephone voice lines and consequently required a modem at each end for signal translation. While simple in concept, the many opportunities for data error that occur when transmitting data through an analog channel, as it requires a relatively complex design.

It was thought that a standard was needed first to ensure reliable communication, and second to enable the interconnection of equipment produced by different manufacturers, thereby fostering the benefits of mass production and competition. From these ideas, the RS232 standard was born. It specified signal voltages, signal timing, signal function, a protocol for information exchange, and mechanical connectors.

If a proprietary or special high-speed transfer method is required by the CNC control, the customer may have to be upgraded to Predator DNC. Unlike the Editor, Predator DNC is designed to support proprietary and special high-speed transfer methods. Refer to our DNC Objects section for more details.

Because modern Laptops and PCs don’t come with Rs232 serial ports any longer, you will need to get a USB to RS232 “Industrial grade” adapter and the proper serial cable to connect from the USB to RS232 adapter to your CNC Machine.

  • Reliable USB to Serial converter
  • Compatible with Windows, plus new & legacy RS232 devices
  • Use with mobile, instrumentation, & point-of-sale applications
  • Great for laptop computers without a serial port
  • CNC Control Compatible

A “Y-Cable” is designed to allow wireless or Ethernet communication to CNC machines, while still allowing access to the external serial port. We often recommend that companies implement these cables as a backup to their DNC system.

If the network goes down, programs can still be transferred into the CNCs manually, without having to open up the machine cabinets and disconnect the DNC system.

No, the Wireless CNC Connect has a DB-9 serial port, but SFA sells those units as a KIT and the KIT includes a 5 ft serial cable that will connect the DB-9 serial port of the wireless CNC Connect to the CNC machines serial port.

Provide the Make and Model of the controls on your CNC machines that you are using the wireless units on and SFA will ship with the proper 5 ft serial cable when the order is placed.