Siemens S5 6ES5470-8MA12 AO and 6ES5464-8MC11 AI Digital Range

Overview

The SIMATIC S5-100U, S5-115U, S5-135U, and S5-155U families accept analog I/O modules from the ET 100U and ET 200U distributed I/O lines as well as the central 6ES5 470 and 6ES5 464 series. Two catalog numbers that surface repeatedly in legacy retrofits are:

• 6ES5470-8MA12 — 2-channel analog output (AO), ±10 V, 1024-unit resolution
• 6ES5464-8MC11 — 4-channel analog input (AI), ±10 V, 2048-unit resolution

Both are floating, opto-isolated, 24 V externally powered modules designed for direct connection to ±10 V transducer and actuator signals. The question most field engineers ask is: what decimal value do I load into the peripheral word, and what decimal value comes back when I read the input? The answer depends on the module's intrinsic resolution (1024 or 2048 units over the bipolar range) and on the SIMATIC S5 left-aligned 16-bit word convention.

This reference consolidates the published specifications for both modules, defines the digital-to-analog and analog-to-digital transfer functions, and provides S5 STEP 5 ladder / statement-list patterns for transferring values between process-image words (PW) and flag words (FW).

Module Identification and Catalog Number Breakdown

Siemens ordering codes follow the 6ES5 nnn-nnnnn structure:

Engineering releases 11 and 12 are within the original S5 hardware generation. Engineering release 21 (e.g. 6ES5464-8MC21) introduced 4–20 mA current ranges and modified settling-time behavior; mixing revision 11/12 firmware with revision 21 firmware on the same bus segment is not supported. Always order matching MLFBs for spares.

6ES5464-8MC11 Analog Input — Specifications

Four differential inputs, software-configurable for 1, 2, or 4 active channels. Each channel is multiplexed into a single integrating ADC.

The 2048-unit resolution refers to the magnitude count over the full bipolar range: ±10 V corresponds to digital values −2048 to +2047 (signed) or 0 to 4095 (offset binary) depending on the CPU's evaluation mode. For an unipolar 0–10 V signal the natural mapping is 0 to +2048 digital, because the negative half of the converter's input range is unused.

6ES5470-8MA12 Analog Output — Specifications

Two independently-isolated voltage outputs suitable for driving position controllers, proportional valves, and chart recorders.

1024-unit resolution means each LSB of digital input corresponds to 10 V / 1024 = 9.766 mV at the output terminals. For unipolar actuator signals biased to 0–10 V the natural mapping is 0 to +1024 digital.

Digital Value Representation — Theory

SIMATIC S5 represents analog values in a 16-bit process-image word using left-aligned format. The most significant bits of the word carry the converted value; the least significant bits are either zero (outputs) or carry status information (inputs).

Bit Layout for a 12-bit ADC (6ES5464-8MC11)

S = sign bit. 0 indicates positive or zero, 1 indicates negative (two's complement).

Bit Layout for an 11-bit DAC (6ES5470-8MA12)

The unused LSBs are written as zero by the CPU when the output word is transferred to the module; the module ignores them.

±10 V Transfer Functions

For the analog input, the analog-to-digital conversion is governed by:

D = round( (V / 10) × 2048 )    6ES5464-8MC11

For the analog output, the digital-to-analog conversion is governed by:

V = (D / 1024) × 10    6ES5470-8MA12

Reference Table — ±10 V Bipolar (both modules)

Reference Table — 0 to +10 V Unipolar (wired to + input, − input grounded)

S5 STEP 5 Programming Patterns

Reading an Analog Input into a Flag Word

    L   PW  128        ; load peripheral input word 128
    T   FW  100        ; transfer to flag word 100
    L   FW  100        ; reload for arithmetic
    SRW 4              ; shift right 4 to right-align 12-bit value
    T   FW  110        ; store right-aligned value in FW 110

The peripheral word address PW 128 corresponds to slot 8 of the central rack (each slot occupies 4 bytes = 2 words). Check the CPU's slot assignment table in the S5-115U manual to confirm the PW starting address for your I/O map.

Writing a Value to an Analog Output

    L   FW  200        ; load scaled value (signed integer)
    SLW 4              ; shift left 4 to left-align into 16-bit word
    T   PW  144        ; transfer to peripheral output word 144

Multiplying or dividing before the SLW 4 allows easy scaling. For example, to command exactly +5.000 V from a flag that holds the user units in millivolts (5000):

    L   FW  200        ; user units, e.g. 5000 mV
    L   KH 0000        ; clear high word
    /   KF +1024       ; 5000 / 1024 = 4 (truncated, scaled to +0.039 V)

Because 1024 units spans 10 V, the scale factor is 102.4 units per volt or 0.00977 V per LSB. Multiply your engineering-unit value by 102.4 to obtain the digital word.

Left-Aligned Word Handling — Why It Matters

S7 and S7-200 modules use right-aligned data; S5 modules use left-aligned data. If you copy a S5 word directly into a S7 FB expecting right-aligned data, your readings will be off by a factor of 16 (a 4-bit shift). Confirm alignment before any cross-platform migration, and apply SRW 4 or SLW 4 as shown above.

Wiring, Pinout, and Shielding

• Both modules use the standard 20-pin front connector with screw or spring terminals.
• Differential inputs on the AI: terminals M0+/M0−, M1+/M1−, M2+/M2−, M3+/M3−. For single-ended 0–10 V, tie the − pin to the module's M-ANA reference terminal.
• AO outputs: Q0+/Q0−, Q1+/Q1−. Observe polarity when driving bipolar loads.
• External 24 V supply must be applied to L+/M on the front connector for the AO module; the AI is backplane-powered.
• Use shielded twisted-pair cable, drain wire bonded at the cabinet end only, max length 200 m. Maintain at least 200 mm separation from VFD power cables.

Configuration Switches and Default Settings

The 6ES5464-8MC11 is software-configured from the S5 CPU's OB1 or OB21 for the number of active channels (1, 2, or 4). No DIP switches are required. The 6ES5470-8MA12 has no user-configurable elements — range, channel count, and update mode are fixed at ±10 V / 2 channels / cyclic update.

For multi-module analog scaling using the FB 251 "ANA-IN" and FB 252 "ANA-OUT" function blocks provided in the S5 standard library, refer to the Siemens manual SIMATIC S5 Programmable Controllers — Standard Function Blocks.

Troubleshooting Matrix

Verification Procedure

1. Apply a calibrated +10.000 V reference to AI channel 0. Read PW 128 in STEP 5 online monitor. Expected value: +2047 (or +2048 for unipolar wiring).
2. Apply 0.000 V (short M+ to M−). Expected value: 0.
3. Apply −10.000 V (reverse polarity of differential source). Expected value: −2048.
4. Force the AO word PW 144 to +1024 from STEP 5. Measure Q0+ to Q0− with DMM. Expected voltage: +10.00 V ±0.05 V.
5. Force the AO word to −1024. Expected voltage: −10.00 V ±0.05 V.
6. Force the AO word to 0. Expected voltage: 0.00 V ±0.01 V.
7. If any reading is off by exactly a factor of 16, apply or remove the SLW 4 / SRW 4 shift as appropriate.

Notes on Migration and Spares

The S5 product line was officially phased out by Siemens with the delivery stop announced in 2014. Spares availability is through stockists and the Siemens Industry Online Support legacy portal. For new installations, the recommended replacement topology is an ET 200SP system with:

• 6ES7531-7KF00-0AB0 (4AI ±10 V, 16-bit, S7-1500 compatible)
• 6ES7532-5ND00-0AB0 (2AO ±10 V, 16-bit, S7-1500 compatible)

When migrating, map the S5 left-aligned 12-bit value (0–2048 for unipolar 0–10 V) to the S7 right-aligned 16-bit raw value by applying a 4-bit left-shift on the S5 side or a 4-bit right-shift on the S7 side before scaling with FC105.

Field-Proven Caveats

• The 6ES5464-8MC11 has an input resistance of only 50 kΩ. High-impedance transducer sources (e.g. pH probes with > 10 MΩ source) must be buffered.
• The 6ES5470-8MA12 cannot drive loads below 3.3 kΩ. A 4 mA–20 mA current loop requires the current-output variant 6ES5470-8MB12 or the universal 6ES5470-7LB12.
• Maximum cable length of 200 m assumes shielded, twisted-pair cable with the shield bonded at one end only. Lengths beyond 200 m require a repeater or a 4–20 mA current loop conversion.
• The 5 V backplane current draw stated in the data sheet is measured at 9 V backplane, not 5 V. This is normal for the S5-115U / S5-135U supplies that output a regulated 9 V DC internally.

FAQ