C94 vs. C76: Which UC300ETH Breakout Board Should You Buy?

If you are building a control cabinet around the UC300ETH Ethernet motion controller, you have two multifunction breakout boards to choose from: the C94 and the C76. Both are made for the UC300ETH, both mount the controller directly on the board, and on paper they look nearly identical. They are not the same board, and the differences line up neatly with the kind of machine you are building.

We sell both, and we get the "which one?" question often enough that it deserves a proper answer. Here it is.

What both boards do

Start with what is shared, because it is most of the board. The UC300ETH on its own is five 26-pin IDC headers and an Ethernet jack. There are no screw terminals, no relays, no spindle speed output, and no charge pump. A multifunction board fixes all of that, and the C94 and C76 fix it the same way:

• The controller mounts on the board. No ribbon cables between the UC300ETH and the breakout board. The Ethernet jack stays accessible, and the board's 10-30VDC supply powers the controller.
• Same port layout. Port 1 is the axis port: 12 outputs for up to 6 axes of step and direction, plus 5 inputs including the E-stop. Port 2 is the input port: 13 optoisolated inputs and 4 outputs. Ports 3, 4, and 5 are IDC26 expansion headers for relay boards, extra breakout boards, or an MPG pendant. All 49 inputs and 36 outputs of the UC300ETH are reachable.
• Same relays. Two electromechanical relays with NO and NC contacts for spindle control and one general-purpose relay that a jumper assigns to Port 2 pin 16 or 17. Tie it to pin 17 and it closes whenever the system is enabled, which is handy for a main contactor or servo power.
• Same spindle speed control. PWM-based 0-10V output for a VFD, with an isolated supply for the spindle circuit generated on the board.
• Same safety logic. A dedicated E-stop terminal tied to the hardware enable line, a microcontroller-based safety charge pump that holds the outputs off until the control software is live, and a driver-fault input.
• Same software. UCCNC natively, Mach3 and Mach4 through the UC300ETH plugin. The UCCNC profile installer configures either board.
• Same mounting approach. Each has its own DIN rail support, and because the controller rides on the board, one support carries the whole assembly.

If you only need the list above, buy the C94 and keep the difference in price. The rest of this article is about the four things the C76 adds and the one thing the C94 does better.

Where the C76 pulls ahead

VFD-fault monitoring. The C76 has a VFD alarm input (5-24VDC, enabled by jumper). When the drive faults, the board drops the enable line and the control software sees an E-stop condition instead of the spindle quietly stopping mid-cut. The C94 monitors E-stop, charge pump, and driver fault, but not the VFD.

High-speed encoder inputs. Port 2 pins 2 through 5 on the C76 are dedicated 5V high-speed inputs for an encoder's A, B, and index signals. That is what you need for a spindle encoder, which is what you need for rigid tapping and threading in UCCNC or Mach4. The C94's inputs are the standard 5-24V optoisolated type with a 2.8 µs delay, which is fine for switches and sensors and not what you want for quadrature.

Pluggable terminals and RJ45 drive cabling. The C76's terminal blocks unplug from the board, so you can pull the board for service without unscrewing forty wires. It is also compatible with the C34 connector board family and the C78 RJ45 shield, which run step, direction, enable, and fault to each drive over a single RJ45 patch cable. On a six-axis servo cabinet that is the difference between an afternoon and a weekend of wiring, and the fault and enable signals come along for free.

Drive enable and disconnect detection. With the C34 boards, the C76 can detect a disconnected drive cable and has a configurable driver-enable polarity. Useful on servo systems, irrelevant on most stepper builds.

Where the C94 pulls ahead

Stronger open-collector outputs. The C94's four open-collector outputs on Port 2 are rated 60VDC at 2A. The C76's are 50VDC at 500mA. In practice that means the C94 will drive a 24V contactor coil, a solenoid valve, or a stack light directly from the board, where the C76 wants a relay in between for anything heavier than a small relay coil.

Price. The C94 is about 20 percent less than the C76 as a bare board, and the UC300ETH + C94 bundle is the lowest-cost complete UC300ETH package we sell.

Simplicity. Fewer jumpers, fewer options, fixed screw terminals. On a hobby router that is a feature.

Side by side

Feature	C94	C76
Controller	UC300ETH, mounts on board	UC300ETH, mounts on board
Axes	Up to 6, step/dir on Port 1	Up to 6, step/dir on Port 1
On-board inputs	18 optoisolated, 5-24VDC	18 optoisolated, 5-24VDC, plus 5V high-speed on Port 2 pins 2-5
Encoder inputs	Not dedicated	Yes, A/B/index at 5V
TTL outputs (Port 1)	12, 5V at 50mA, 400kHz	12, 5V, 400kHz
Open-collector outputs (Port 2)	4, 60VDC at 2A	4, 50VDC at 500mA, 250kHz
Relays	3 (2 spindle, 1 general), 2A at 125VAC or 60VDC	3 (2 spindle, 1 general)
Spindle speed	PWM-based 0-10V, isolated	PWM-based 0-10V, isolated
Monitors	E-stop, charge pump, driver fault	E-stop, charge pump, driver fault, VFD fault
Terminals	Fixed screw-on	Pluggable screw-on
Drive connection options	Screw terminals	Screw terminals, C77 terminal shield, or C78/C34 RJ45 boards
Expansion ports	3 IDC26 (LPT3, LPT4, LPT5)	3 IDC26 (LPT3, LPT4, LPT5)
Analog port	2 in, 2 out, 0-5V, not isolated	2 in, 2 out, not isolated
Power	10-30VDC, 2A minimum	10-30VDC, 700mA plus loads
DIN rail support	DIN Rail Support for C94	DIN Rail Support for C76
Software	UCCNC, Mach3, Mach4	UCCNC, Mach3, Mach4
Board only	C94 board	C76 board
With controller	UC300ETH + C94 bundle	UC300ETH + C76 bundle
User manual	C94 manual (PDF)	C76 manual (PDF)

Input and output counts are the same on both boards because they come from the controller, not the board. The UC300ETH has 49 inputs and 36 outputs across its five ports; the breakout board decides how many of them land on terminals (Ports 1 and 2) and how many wait on expansion headers (Ports 3, 4, and 5).

Pick by machine, not by spec sheet

Stepper-driven CNC router. C94. You need six axes at most, a handful of limit and home switches, a probe, a VFD with on/off and 0-10V speed, and maybe a relay or two for dust collection and coolant. The C94 does all of it, and its 2A outputs will switch the dust collector contactor directly.

Plasma table. C94, paired with an external torch height controller such as the THC-1 or THC-2. The THC talks to the board through ordinary inputs and outputs, so the C76's extras do not buy you anything here. Spend the difference on the THC.

Laser or engraver. C94. PWM, a relay for the laser supply enable, and a few inputs.

Mill or lathe retrofit on steppers, no spindle encoder. Either. The C94 is cheaper. Go C76 if you want VFD-fault monitoring, which matters more on a mill where a stalled spindle under a cutter is expensive.

Anything with a spindle encoder. C76. Rigid tapping, threading on a lathe, and spindle-synchronized moves all need the high-speed encoder inputs.

Servo drives. C76. The C34 boards and RJ45 cabling carry step, direction, enable, and fault to each drive on one patch cable, and the board's drive-fault and cable-disconnect handling is built for exactly this. You can wire servos to a C94 with screw terminals and discrete fault inputs; it just takes longer and you give up the disconnect detection.

Production cabinet someone else will service. C76. Pluggable terminals mean the board comes out without disturbing the field wiring.

Two things people get wrong

The DIN rail supports are not interchangeable. The C94 and C76 are different sizes. The C94 support fits the C94, the C76 support fits the C76, and either one carries the controller along with the board. You never need a separate support for the UC300ETH when it is mounted on one of these boards.

You do not need a separate 5V supply for the controller. A bare UC300ETH needs 5V. Mounted on a C94 or C76, it gets that from the board, which runs on 10-30VDC. One 24V DIN rail supply covers the board, the controller, your sensors, and the relay coils.

Common questions

Is the C94 a newer version of the C76?
No. They are parallel products aimed at different builds. The C76 is the fuller-featured board; the C94 is the simpler, lower-cost one. Both are current.

Does the C94 or C76 work with the Ethernet SmoothStepper or PoKeys57CNC?
No. Both are built for the UC300ETH and the controller mounts directly on the board. For the Ethernet SmoothStepper, use the C25XP.

Can I run Mach3 or Mach4 instead of UCCNC?
Yes. The UC300ETH has plugins for both. The board does not care which software is driving it. A sample Mach3 XML profile for the C94 is on the product page, and the UCCNC profile installer configures either board.

How many axes do I get?
Up to six on either board. Port 1 carries 12 outputs, which is six step and direction pairs.

Can I add more inputs and outputs later?
Yes, on either board. Ports 3 and 5 are input expansion headers and Port 4 is an output expansion header. Relay boards and additional breakout boards plug in with IDC26 ribbon cables.

Which one for a 4x8 router on NEMA 34 steppers?
C94. Size of the machine does not change the answer; the drive type and the spindle do.

I already own a UC300ETH. Which listing do I buy?
The board on its own: C94 or C76. The bundles are for people who need the controller as well.

Where to go from here

• C94 UC300ETH Multifunction CNC Breakout Board and the UC300ETH + C94 bundle
• C76 UC300ETH Multifunction CNC Breakout Board and the UC300ETH + C76 bundle
• UC300ETH-5LPT Ethernet motion controller on its own
• User manuals with full pinouts and wiring samples: C94 (PDF) and C76 (PDF)
• All CNC motion controllers and breakout boards

Still not sure? Send us the drive model, spindle setup, and software you plan to run and we will tell you which board to order.