Using Heidenhain Scales with TouchDRO

How to Identify Your Scale's Signal Type

Heidenhain incremental scales come with several connector styles. Older 11 µA_pp current-signal scales typically use a 9-pin M23 round connector. Most 1 V_pp and TTL scales use a 12-pin M23, but Heidenhain also used encoder-side 15-pin D-sub connections for both interfaces. The connector is a useful clue, but it does not identify the signal type by itself. Confirm the interface from the scale model number before wiring.

The most reliable way to determine the output type of your scale is to decode the model number. Heidenhain linear-scale model numbers follow a consistent scheme: two letters, a three-digit number, and sometimes a trailing letter, such as LS 487 C.

For wiring, the middle digit is the important one: it tells you the scale's output signal type. For example, LS 487 is a 1 V_pp scale, LS 477 is a TTL scale, and LS 303 C is an 11 µA_pp scale with distance-coded reference marks. A trailing letter, where present, flags the reference-mark or control-interface variant. C marks distance-coded reference marks; TouchDRO does not decode the mark spacing, but it can use an individual mark as an ordinary reference pulse. F, M, P, and S identify control-specific interfaces for Fanuc, Mitsubishi, Panasonic, and Siemens controls.

Middle Digit	Signal Type	What You Need for TouchDRO
0	11 µApp current	Heidenhain EXE box, then TTL adapter cable
1	EnDat 2.2 pure serial	Not currently supported
2 or 7	TTL square-wave	Adapter cable
8	1 Vpp sin/cos	TouchDRO converter or Heidenhain IBV box
9	Other absolute interface	Not currently supported

Digit 2 marks TTL without built-in interpolation; digit 7 marks TTL with internal interpolation. Both connect to TouchDRO the same way. Digit 8 can appear on a pure 1 V_pp incremental scale or on an EnDat scale that also provides 1 V_pp incremental signals. TouchDRO cannot read EnDat position data, but it can use the incremental signals through the converter.

Heidenhain incremental scales include one or more reference marks that let a readout recover absolute position after a power cycle. TouchDRO treats each reference mark as a single pulse, regardless of whether the scale uses one fixed mark, several selectable marks, or the distance-coded pattern found on C-suffix scales. TouchDRO does not decode the distance-coded spacing, but it doesn’t need to: as long as the mark produces a repeatable pulse at the same physical location, it works.

1 Vpp Sin/Cos Scales

Modern Heidenhain linear scales, such as the LS 187, LS 487, LS 186, and LS 486, output an analog sin/cos differential signal at 1 V_pp amplitude and run on a 5 V supply. These scales come on a 12-pin M23 connector or a 15-pin D-sub. The table below gives the encoder-side pinout for each.

Signal	Wire Color	12-pin M23	15-pin D-sub
A+	Brown	5	1
A−	Green	6	9
B+	Gray	8	3
B−	Pink	1	11
R+	Red	3	14
R−	Black	4	7
+5 V (Up)	Brown/Green	12	4
Sensor Up	Blue	2	12
0 V	White/Green	10	2
Sensor 0 V	White	11	10

A 15-pin D-sub on a Heidenhain readout or interface box uses a different pinout for the same signals. The column above is the arrangement Heidenhain documents for the encoder side.

To connect a 1 V_pp scale to TouchDRO, the signal must be converted to 5 V quadrature (differential or single-ended). You have two options: a Heidenhain IBV interpolation box, or a TouchDRO sin/cos-to-quadrature converter. The tradeoffs between the two choices are explained in the Converter or Interpolation Box section.

Converter or Interpolation Box?

The TouchDRO sin/cos-to-quadrature converter does 1:1 conversion from sin/cos signal to a quadrature signal with the same period. In other words, a 20 μm sin/cos scale can resolve 5 μm, since for every quadrature period there are 4 distinct edges TouchDRO can count. An interpolation box subdivides each period further: 5-fold interpolation on that same scale gives 1 μm, and 10-fold gives 0.5 μm.

While more resolution might seem like the obvious choice, there is a subtle but important tradeoff to consider. Interpolation accuracy depends on a clean sin/cos signal. Optical scales degrade with age as gratings pick up contamination and scanning LEDs dim, and interpolation accuracy degrades with them. A zero-crossing converter only cares where the signal crosses zero, which is far less sensitive to amplitude drift.

In practice, if you are planning to use your scales on a milling machine or a lathe, 5 μm resolution from the 1:1 converter is more than adequate. On the other hand, if this is for a precision surface grinder, a jig borer, or similar equipment, and the scale is in good condition, a 5x or 10x interpolation box (Heidenhain IBV 101) is the better choice.

TTL Square-Wave Scales

Heidenhain makes scales that output a differential quadrature signal in one of two forms, TTL or HTL. TTL scales run on a 5 V supply at 5 V logic levels and are electrically compatible with TouchDRO. Heidenhain's literature often calls these scales "digital," which should not be confused with its absolute scales, which report position over a serial protocol.

Heidenhain documents the TTL interface on a 12-pin M23 connector and a 15-pin D-sub. The table below gives the encoder-side pinout for each.

Signal	Wire Color	12-pin M23	15-pin D-sub	TouchDRO Line
Ua1	Brown	5	1	Channel A
Ua1 (inverted)	Green	6	9	Channel A (inverted)
Ua2	Gray	8	3	Channel B
Ua2 (inverted)	Pink	1	11	Channel B (inverted)
Ua0 (reference)	Red	3	14	Reference
Ua0 (reference, inverted)	Black	4	7	Reference (inverted)
UaS (fault)	Violet	7	13	—
+5 V (Up)	Brown/Green	12	4	+5 V
Sensor Up	Blue	2	12	+5 V
0 V	White/Green	10	2	0 V
Sensor 0 V	White	11	10	0 V

The table above gives the encoder-side pinout. Heidenhain readouts and interface boxes use a different 15-pin D-sub pinout for the same signals, so make sure you are tracing the scale, not the equipment it was wired to. Before you modify a connector or wire a scale into TouchDRO, confirm from the model number that it is actually a TTL scale. Heidenhain is consistent with wire colors across scale models and generations, so if a pin number is in doubt, the wire color is the more reliable guide.

11 µApp Current-Signal Scales

11 µA_pp is Heidenhain's older analog interface, found on scales like the LS 303, LS 603, and similar models from the era before the 1 V_pp standard. These scales output an extremely low-level current signal rather than a voltage signal. The signal is too weak to drive a DRO input directly, so it must first be converted to TTL quadrature using a Heidenhain EXE box. Once converted, the EXE's TTL output connects to TouchDRO with the same adapter cable used for a native TTL scale.

M23 9-Pin Connector and Pinout

11 µA_pp scales use a 9-pin M23 connector, recognizable by its larger center pin. A 9-pin connector by itself does not guarantee an 11 µA_pp scale, so confirm the interface from the model number rather than the connector alone.

Signal	Wire Color	9-pin M23
I1+	Green	1
I1−	Yellow	2
I2+	Blue	5
I2−	Red	6
I0+ (reference)	Gray	7
I0− (reference)	Pink	8
+5 V (Up)	Brown	3
0 V	White	4
Internal shield	White/Brown	9
Cable shield	—	Housing

Heidenhain readouts and interface boxes that accept 11 µA_pp scales use various D-sub connectors with different pinouts. Those are equipment-side connectors, not scale-side. If you are rewiring a D-sub-terminated 11 µA_pp installation, trace the actual wires back to the scale rather than assuming any particular D-sub pinout.

EXE Interpolation Boxes

The most common EXE models are listed below. An EXE 101 with 5x interpolation is sufficient for most machine-shop applications. Higher interpolation factors follow the same tradeoffs described in the 1 V_pp converter section.

Model	Interpolation	Notes
EXE 101	5- or 10-fold	Current production (IP65)
EXE 102	20/25/50/100-fold	Current production (IP65)
EXE 602 E	No interpolation or 5-fold	Common on the used market
EXE 610C / 611 / 612	5- or 10-fold	Older box designs
EXE 660 B	25/50/100/200/400-fold	Older box design

Absolute and HTL Interfaces

Not every Heidenhain scale is incremental. Heidenhain also makes absolute scales (such as the LC series) that report position over the EnDat or SSI serial interface, and HTL scales that output a higher-voltage quadrature signal. TouchDRO does not currently support any of these interfaces.

If you have an EnDat, SSI, or HTL Heidenhain scale and would like to use it with TouchDRO, please contact us. Knowing there is demand helps us prioritize what to support next.

Common Wiring Notes

• Identify the interface first. Heidenhain has used several connector styles, and the 12-pin M23 in particular is shared between 1 V_pp and TTL scales. Confirm the interface from the scale's ordering designation before wiring — the connector alone tells you nothing about what's on the pins.
• Verify the supply before powering. Heidenhain incremental scales run on a regulated 5 V supply. Getting +5 V and 0 V right matters — reversed polarity can damage a scale instantly.
• Handle the sensor lines. Sensor Up and Sensor 0 V are remote voltage-sense lines, not extra signals. On a short adapter cable, tie them to Up and 0 V respectively at the connector.
• Keep differential pairs together. Each A+/A−, B+/B−, and R+/R− pair (or U_a1, U_a2, U_a0 pair for TTL) should stay on a twisted pair inside the adapter cable, with the shield bonded to the connector housing.
• Insulate unused wires. Leave vacant wires unconnected, but isolate each bare end individually — an unterminated wire that shorts against a pin or the housing can damage the scale.

Frequently Asked Questions

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How do I tell which interface my Heidenhain scale uses?

You can't reliably tell from the connector. Heidenhain's 1 Vpp sin/cos and TTL square-wave scales are commonly found on the same 12-pin M23 round connector — and both also appear on a 15-pin D-sub — so the connector alone won't distinguish them. The interface is encoded in the scale's ordering designation, so check the model number and label on the scale body. Older 11 µApp current-signal scales commonly use a 9-pin M23 connector, but a 9-pin connector on its own doesn't guarantee an 11 µApp scale either. If you're still unsure, a quick check with an oscilloscope settles it: a 1 Vpp scale shows roughly 1 V sine waves on the A and B lines, while a TTL scale shows 5 V square waves.

My Heidenhain scale has a 12-pin round connector — is it 1 Vpp or TTL?

It could be either. The 12-pin M23 connector is shared between Heidenhain's 1 Vpp sin/cos scales and its TTL square-wave scales, and the pin assignments are different between the two. Identify the scale by its ordering designation before wiring anything, because a 1 Vpp scale needs a converter while a TTL scale only needs an adapter cable — they are not interchangeable.

What resolution will I get from a 1 Vpp scale with TouchDRO?

Through the TouchDRO 1 Vpp converter, which works as a 1:1 zero-crossing comparator, you get four counts per signal period — one quarter of the scale's grating period. A scale with a 20 µm signal period gives an effective resolution of 5 µm. If you need finer resolution, a Heidenhain IBV interpolation box can subdivide the 1 Vpp signal much further before it reaches TouchDRO.

Can TouchDRO read an 11 µApp scale directly?

No. The 11 µApp interface outputs a very low-level sinusoidal current signal that can't drive a DRO input. It needs interpolation and digitizing electronics — a Heidenhain EXE box — to convert it into a TTL square-wave signal first. The EXE's TTL output then connects to TouchDRO with the same adapter cable used for native TTL scales.

What are the Sensor lines on the connector for?

The Sensor Up and Sensor 0 V lines are remote voltage-sense lines. They let the driving electronics measure the actual supply voltage at the scale and compensate for voltage drop over a long cable. Inside the scale they are connected to the corresponding power line. On a short adapter cable they can be tied to Up and 0 V respectively at the connector.

Can I use a Heidenhain scale with a DRO other than TouchDRO?

It depends on the signal type. TTL scales output a standard RS-422 differential quadrature signal that works with any DRO that accepts it. A 1 Vpp scale run through a converter or an interpolation box also ends up as standard TTL quadrature, so it will work the same way. An 11 µApp scale needs a Heidenhain EXE box first, after which it behaves like a TTL scale. The absolute EnDat and SSI interfaces use serial protocols that are generally not supported by aftermarket DROs, TouchDRO included.

The connector on my Heidenhain scale doesn't match anything on this page — what is it?

Heidenhain supplies scales and encoders to many machine-tool and measurement-equipment manufacturers, and those are often fitted with OEM-specific connectors or pigtail harnesses that won't match the standard M23 connectors shown here. Send us a photo of the scale, its label, and the connector and we'll help you identify it and work out the wiring.