Overview
The ET 200S distributed I/O system supports serial communication through the 1SI (Serial Interface) module, which is inserted in the terminal slot of an IM 151 interface module. Engineers frequently confuse the two product variants of the 1SI — the 6ES7138-4DF01-0AB0 (ASCII/3964R protocol) and the 6ES7138-4DF11-0AB0 (Modbus/USS protocol) — because some legacy manuals list the wrong protocol family against the wrong order number. This article clarifies the compatibility, firmware, and configuration constraints for the ASCII/3964R variant when used with the IM 151-3PN (PROFINET interface module, e.g., 6ES7151-3BA23-0AB0 or 6ES7151-3BB23-0AB0) and provides a commissioning checklist for PC-coupled serial traffic.
Module Identification and Part Number Matrix
| Order Number (MLFB) | Protocol Family | Firmware | Successor | Status |
|---|---|---|---|---|
| 6ES7138-4DF00-0AB0 | ASCII/3964R | v1.0 | DF01 | Phased out |
| 6ES7138-4DF01-0AB0 | ASCII / 3964(R) | v1.3 (product release 5) | — | Active |
| 6ES7138-4DF10-0AB0 | Modbus / USS | v1.0 | DF11 | Phased out |
| 6ES7138-4DF11-0AB0 | Modbus / USS | v1.3 | — | Active |
The ASCII variant (DF01) is intended for free-form ASCII frame transmission and for the Siemens 3964(R) handshake protocol. The Modbus/USS variant (DF11) cannot be re-flashed to ASCII mode and vice versa — the protocol engine is bound to the firmware delivered with the module.
IM151-3PN Compatibility Requirements
According to the official Siemens List of I/O Modules for Use with ET 200S IM151-3PN High Speed (entry dated 02.07.2012), the 1SI 3964(R)/ASCII module 6ES7138-4DF01-0AB0 is listed as a supported I/O module with firmware V1.3 and product release 5 for the IM151-3PN High Speed. Older documentation that states "not supported up to product release 4" is correct — the constraint is purely on the minimum product release of the 1SI, not the IM.
Supported ET 200S interface modules (PROFINET side) for the 1SI ASCII/3964R module include:
- 6ES7151-3BA23-0AB0 — IM 151-3PN
- 6ES7151-3BB23-0AB0 — IM 151-3PN High Speed
- 6ES7151-3AA23-0AB0 — IM 151-3PN FO
Refer to the generic What should you watch out for regarding the compatibility of I/O modules and interface modules when configuring an ET 200S? entry for the full matrix.
Hardware Configuration in STEP 7 / TIA Portal
- Open the project in STEP 7 V5.5 / TIA Portal V13 or later.
- Insert the IM 151-3PN (or 3PN HS) into the PROFINET subnet and assign a device name and IP address (default 0.0.0.0 → assign via "Assign PROFINET device name").
- Open the device view of the ET 200S station. The 1SI 6ES7138-4DF01-0AB0 must appear in the hardware catalog under ET 200S > I/O modules > Serial. If the module is not visible, the HSP (Hardware Support Package) is not installed.
- Drag the 1SI module into the slot immediately to the right of the IM. The slot index determines the diagnostic address; the module occupies 16 input bytes and 16 output bytes for data plus a separate diagnostic address.
- Open the module's properties and select protocol = ASCII (not 3964R) for PC-coupling, or 3964R when communicating with a Siemens S5 / third-party 3964R device.
- Compile and download the hardware configuration to the S7 CPU (or the IM 151-3PN acting as a PROFINET device on a higher-level controller).
Required Hardware Support Packages (HSP)
| Portal Version | Required HSP | Module Listed As |
|---|---|---|
| STEP 7 V5.5 + SPx | HSP 0226 / later | 1SI ASCII/3964R |
| TIA Portal V13 | HSP for ET 200S V3.0 | 6ES7 138-4DF01-0AB0 |
| TIA Portal V15 / V16 / V17 | Default catalog (no extra HSP needed on most installations) | 1SI ASCII/3964R V1.3 |
When the module is missing from the catalog after a clean install, install the latest ET 200S HSP from the Siemens support portal. Documentation for the catalog selection is referenced in the ET 200SP / ET 200S manual collection.
Firmware Release Constraints
The 1SI 3964(R)/ASCII module is accepted by the IM 151-3PN starting from product release 5 of the 1SI module. Older 1SI modules (release 1–4) are not recognized by current IM 151-3PN firmware and will generate the diagnostic buffer entry "Module does not match the configured module" (SF LED on, BF LED behavior depends on the configuration). The product release is printed on the module's label, e.g., "FW: V1.3 / Release 5".
If the module is older than release 5, it can be flashed using the Siemens Field PG and a TIA Portal / STEP 7 firmware update over the backplane bus. The flash image is part of the standard TIA Portal installation and is selected as 1SI 3964R/ASCII V1.3.
ASCII / 3964R Communication Parameters
| Parameter | Setting Range | Typical PC Default |
|---|---|---|
| Baud rate | 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 76800 bit/s | 9600 bit/s |
| Data bits | 7 or 8 | 8 |
| Parity | None / Even / Odd | None |
| Stop bits | 1 or 2 | 1 |
| Flow control | None / XON-XOFF / RTS-CTS (3964R only) | None |
| End delimiter (ASCII) | Configurable: CR / LF / CR+LF / ETX / user-defined 1–2 bytes | CR+LF |
| Frame length (ASCII) | 1–1024 bytes | ≤ 1024 |
| Receive buffer | 1024 bytes per direction | — |
The parameters must match the partner device (PC COM port or USB-to-serial converter) exactly. A single bit of mismatch in parity or stop bits will cause the 1SI to raise diagnostic interrupt "Framing error" and discard the frame.
PC-Side Serial Communication Setup
When the partner is a PC running a terminal program, sample program, or SCADA serial driver, the connection is wired as follows on the D-sub connector of the 1SI (RS-232C, male, 9-pin):
| 1SI Pin (DB-9M) | Signal | PC DB-9F | Note |
|---|---|---|---|
| 2 | RxD (received by 1SI) | 3 (TxD) | Cross |
| 3 | TxD (sent by 1SI) | 2 (RxD) | Cross |
| 5 | SGND (signal ground) | 5 | 1:1 |
| 7 | RTS (1SI → PC) | 8 (CTS) | Cross if hardware handshake |
| 8 | CTS (PC → 1SI) | 7 (RTS) | Cross if hardware handshake |
For null-modem / three-wire ASCII traffic, only pins 2, 3, and 5 are needed. Pins 7 and 8 must not be bridged on either side if hardware handshake is disabled — the 1SI interprets a held-CTS as "partner not ready" and freezes transmission.
Sample S7 Logic — Send a Free-Form ASCII Frame
// S7-300/400 STL or SCL excerpt
// DB "1SI_DB".SEND_BUFFER := 'HELLO,PLC!\r\n'; // 12 bytes
// Trigger send:
"1SI_DB".SEND_REQ := TRUE;
"1SI_DB".SEND_LEN := 12;
// The 1SI raises "DONE" or "ERROR" on the diagnostic byte.
IF "1SI_DB".SEND_DONE THEN
"1SI_DB".SEND_REQ := FALSE;
END_IF;
If the partner reports that it "received no data from the PC", the fault is in 80 % of cases a wiring or parameter mismatch on the PC side, not in the S7 program. Verify the PC COM port number, the cable pinout, and the COM port's FIFO / 16550-compatible mode in the Windows Device Manager.
Diagnostic Interrupt and SF LED Behavior
| SF LED | BF LED | Diagnostic Byte (hex) | Meaning | Action |
|---|---|---|---|---|
| Off | Off | 0x00 | Normal operation | — |
| On | Off | 0x01 | Configuration error (slot mismatch) | Check HW config order number |
| On | Off | 0x05 | Module firmware too old | Flash to V1.3 (release ≥ 5) |
| Off | On | 0x06 | Lost partner / no receive clock | Check cable and partner device |
| Flashing | — | 0x07 | Framing / parity error on incoming frame | Verify baud, parity, stop bits |
| On | On | 0x0A | Watchdog timeout (no process ack from CPU) | Check PROFINET connection to IM |
The diagnostic byte is read via SFC 13 / SFB 54 ("DPNRM_DG") on PROFIBUS systems or via the standard PROFINET record ("Get diagnostics", index 0x8000) for the 1SI's slot.
Troubleshooting Matrix
| Symptom | Likely Root Cause | Verification | Fix |
|---|---|---|---|
| Module not visible in HW catalog | HSP not installed / wrong Portal version | Search catalog for "6ES7 138-4DF01" | Install latest ET 200S HSP |
| SF LED on, online diagnostics "wrong module" | Manual ambiguity — DF01 selected but DF11 physically installed (or vice versa) | Read MLFB from physical label | Replace with matching protocol variant |
| SF LED on, "firmware update required" | 1SI release < 5 | Read firmware in online → module information | Flash 1SI to V1.3 |
| PC receives no data from PLC | Wrong DB used, SEND_REQ never set, or partner COM port closed | Watch SEND_REQ and DONE in VAT table | Trigger send in OB1 / cyclic OB |
| PLC receives no data from PC | Cable crossed but PC's hardware handshake disabled; or 1SI configured for 3964R but PC sends raw ASCII | Loopback test (pin 2↔3 on PC side) | Switch protocol to ASCII, match parameters |
| Garbled data on both sides | Baud rate / parity mismatch | Read back configured parameters from 1SI | Make partner settings match 1SI |
| Sporadic dropped frames > 256 bytes | Frame length exceeds configured length or buffer overflow | Inspect receive buffer length register | Increase frame length or split messages |
Verification Procedure
- Inventory check: Confirm the front label of the 1SI module reads 6ES7138-4DF01-0AB0 and firmware V1.3 / release 5 or higher.
- Catalog check: In STEP 7 / TIA Portal, the 1SI ASCII/3964R module must be selectable for the IM 151-3PN slot. If absent, install the matching HSP.
- Compile and download: Download the HW config to the CPU and IM. The 1SI SF LED must be off after power-up.
- Loopback test: Bridge pin 2 to pin 3 on the 1SI DB-9 connector and trigger a send from the S7 program. The 1SI must echo the frame back into the receive buffer. If not, the module or its parameter block is faulty.
- PC test: Connect a known-good USB-to-RS232 cable to a PC running a terminal program set to 9600/8/N/1. Send a short ASCII string terminated with CR+LF. The S7 program must detect the end delimiter and store the frame in the receive DB.
- End-to-end test: Send an application-level command and confirm the PLC response on both sides within the configured timeout (default 5 s for 3964R; user-defined for ASCII).
Notes on Migration and Obsolescence
The 1SI 6ES7138-4DF01-0AB0 is the long-standing ASCII/3964R module for ET 200S. The 1SI variant is not present in the ET 200SP or ET 200MP families — those use the CM PtP (point-to-point communication module) or the ET 200SP F-CM for serial traffic. If a future migration to ET 200SP is planned, the protocol-specific application code (frame parsing, delimiter handling, 3964R handshake) must be rewritten against the CM PtP API; the 1SI's SFC / SFB-based interface is not portable.
For new installations, evaluate the ET 200SP CM PtP (6ES7137-6AA00-0BA0, RS-232/422/485) or the CM 4xRS232 (6ES7540-1AD00-0AA0) for S7-1500. The 1SI remains the correct choice only when the controller is S7-300 / S7-400 / ET 200S and the application already uses the SFB 60/SFB 61 interface.
Is the 1SI 6ES7138-4DF01-0AB0 supported by the IM 151-3PN?
Yes. The 6ES7138-4DF01-0AB0 (ASCII/3964R, firmware V1.3, product release 5) is listed in the official Siemens compatibility list as a supported module for the IM 151-3PN High Speed. Earlier product releases (1–4) are not supported and must be flashed to V1.3.
What is the difference between 6ES7138-4DF01-0AB0 and 6ES7138-4DF11-0AB0?
DF01 is the ASCII/3964R protocol variant; DF11 is the Modbus/USS protocol variant. They are not firmware-upgradable to each other. Always select the order number that matches the required protocol in STEP 7 / TIA Portal and verify the label on the physical module.
Why does the manual list 4DF01 as Modbus/USS?
Some legacy manuals (and certain translated editions) contain an error. The correct mapping is 4DF01 → ASCII/3964R and 4DF11 → Modbus/USS. Cross-check with the order number on the front label and with the current Siemens online catalog entry.
My PC receives no data from the PLC. What should I check first?
Verify (1) the cable pinout (2↔3 cross, 5↔5 ground), (2) that the partner COM port number in the PC application matches the physical port, (3) baud rate / parity / stop bits match the 1SI configuration exactly, and (4) that SEND_REQ is being set in the S7 program. A loopback test (bridging 2↔3 at the 1SI) confirms the module itself is functional.
Can the 1SI module be replaced by an ET 200SP CM PtP module?
No direct one-to-one replacement. The 1SI is a slot module in the ET 200S terminal row, while the ET 200SP CM PtP is a separate station behind an IM 155-6. Both support ASCII and 3964R, but the application code (SFB 60/61 vs. PtP block library) must be rewritten. The 1SI remains the correct choice for ET 200S and S7-300/400 systems.