Overview
The Siemens Field PG M5 is the latest generation of Siemens portable programming devices used to commission, diagnose, and program SIMATIC S5, S7, and SINUMERIK controllers. Depending on the ordered MLFB (order number), the integrated COM1 connector is implemented either as a pure V.24 (RS-232-C) interface or as a combined V.24/TTY port with hardware support for 20 mA current loop signaling required by older S5 AG (Automation Devices) and PG (Programming Device) cables.
This reference explains the electrical difference between V.24 and TTY, maps the 25-pin and 9-pin pinouts, identifies which Field PG MLFBs carry the TTY hardware, and clarifies whether the legacy S5 programming cable shipped with a PG 710 can be reused on a current-generation Field PG.
V.24 / RS-232 and TTY 20 mA Technical Background
Two fundamentally different physical layers appear on Siemens programming cables:
- V.24 (RS-232-C) – voltage-based interface defined in ITU-T V.24 and EIA/TIA-232-E. Logic 1 = −3 V to −15 V (MARK), logic 0 = +3 V to +15 V (SPACE). Maximum cable length is limited to about 15 m at 19.2 kbit/s. Refer to the serial port overview for historical context.
- TTY 20 mA current loop – current-based interface, optically isolated on the receiver side. Logic 1 = 20 mA loop current flowing, logic 0 = loop current interrupted. Originally specified in Siemens AG documentation for SIMATIC S5 PG interfaces, allowing cable runs up to 1000 m in electrically noisy environments.
The two physical layers are not electrically compatible. A passive cable cannot convert between them; an active converter such as the Phoenix Contact PSM-ME-RS232/TTY-P (order 2744458) is required. This converter translates a V.24 (RS-232) interface into a 20 mA TTY current loop bidirectionally, with optical isolation to suppress industrial interference.
Field PG M5 Variants and MLFB Identification
The Field PG M5 family is ordered under the MLFB prefix 6ES7717-1B.... The trailing block determines whether the device carries the S5 hardware option, which in turn dictates whether COM1 supports TTY.
| MLFB (excerpt) | S5 Online Interface | S5 Prommer (EPROM) | COM1 Implementation |
|---|---|---|---|
| 6ES7717-1BB02-0BB4 | No | No | V.24 (RS-232) only, DB-25 female |
| 6ES7717-1BB0x-0BBx (with S5 option) | Yes | Yes (depending on sub-variant) | V.24 + TTY 20 mA, shared DB-25 female |
On a unit without the S5 option, the 25-pin connector exposes only the standard V.24 signals (TD, RD, RTS, CTS, DSR, DTR, DCD, RI) plus chassis ground. The TTY pins are physically unwired because the mainboard lacks the current-loop transceiver.
Pinout of the DB-25 COM1 Connector
When the Field PG COM1 is configured as V.24, the DB-25 female pinout follows the EIA-232 DTE convention:
| Pin | Signal (V.24 / RS-232) | Direction (DTE = PG) | Notes |
|---|---|---|---|
| 1 | Shield / Protective Ground | — | Chassis bond |
| 2 | TXD (Transmitted Data, SD) | Output | Data from PG to PLC |
| 3 | RXD (Received Data, RD) | Input | Data from PLC to PG |
| 4 | RTS (Request To Send) | Output | Handshake |
| 5 | CTS (Clear To Send) | Input | Handshake |
| 6 | DSR (Data Set Ready) | Input | Modem signal |
| 7 | Signal Ground (GND) | — | Common return |
| 8 | DCD (Data Carrier Detect) | Input | Modem signal |
| 20 | DTR (Data Terminal Ready) | Output | Modem signal |
| 22 | RI (Ring Indicator) | Input | Modem signal |
For basic 3-wire point-to-point links, only pins 2, 3, and 7 are used. Handshaking lines (4/5, 6/20) can be looped back or pulled to valid levels for many Siemens protocols, but STEP 5 online protocols typically require the full handshake set.
TTY Pins on S5-Equipped Field PG
On a Field PG M5 with the S5 option, the same DB-25 connector carries additional TTY signals. The Siemens convention for the 20 mA current loop uses:
| Pin | TTY Signal | Description |
|---|---|---|
| 13 | TTY Tx+ (20 mA source) | Current loop transmit, positive |
| 14 | TTY Tx− (return) | Current loop transmit, return |
| 15 | TTY Tx+ shield / reserved | Loop shield |
| 18 | +5 V supply for active cable (PG 7xx) | Some legacy TTY cables |
| 19 | TTY Rx+ (20 mA source) | Current loop receive, positive |
| 21 | TTY Rx− (return) | Current loop receive, return |
| 25 | TTY loop shield / reserved | Loop shield |
PG 710 S5 Cable Compatibility with Field PG M5
The original question concerns the S5 programming cable that was delivered with a PG 710 (Siemens MLFB 6ES5 785-1xxx series). That cable was a passive RS-232 ↔ TTY adapter designed for the PG 710's TTY-capable serial port.
Reuse on a Field PG M5 depends entirely on which MLFB is installed:
| Field PG M5 MLFB | PG 710 S5 Cable Reuse | Reason |
|---|---|---|
| With S5 option (e.g., 6ES7717-1BB0x with S5 online) | Yes, when cable has DB-25 male on PG side | Mainboard TTY hardware is present; signals line up |
| Without S5 option (e.g., 6ES7717-1BB02-0BB4) | No | TTY pins are not driven by mainboard; cable termination has no effect |
For the specific MLFB 6ES7717-1BB02-0BB4, the unit is ordered without S5 online interface and without S5 prommer. COM1 is implemented as V.24 only, so the PG 710 cable cannot be reused. STEP 5 can still run on this unit in the pre-installed Windows sandbox, but online communication to an S5 PLC requires a converter such as the Phoenix Contact PSM-ME-RS232/TTY-P.
DB-25 to DB-9 Adapter Shipped with the Field PG
Siemens ships a passive DB-25 female to DB-9 male adapter with every Field PG. This adapter maps the standard V.24 signals so that off-the-shelf RS-232 cables with DB-9 connectors can be plugged in. The mapping is:
| DB-25 Pin (PG side) | DB-9 Pin (Cable side) | Signal |
|---|---|---|
| 2 | 3 | TXD |
| 3 | 2 | RXD |
| 4 | 7 | RTS |
| 5 | 8 | CTS |
| 6 | 6 | DSR |
| 7 | 5 | Signal Ground |
| 8 | 1 | DCD |
| 20 | 4 | DTR |
| 22 | 9 | RI |
With this adapter in place, a standard 9-pin RS-232 null-modem cable connects the Field PG to a SINUMERIK, SIMATIC panel, or any V.24-speaking DCE device.
Using TTY with a V.24-Only Field PG
If your workflow requires talking to an S5 PLC (AS 511 protocol over 20 mA loop) and the Field PG has no S5 option, use an external converter between the PG COM1 (V.24) and the S5 PG cable (TTY):
- Connect the DB-25 COM1 of the Field PG to the RS-232 (V.24) side of the Phoenix Contact PSM-ME-RS232/TTY-P (order 2744458).
- Connect the TTY side of the converter to the S5 PG cable that goes to the PLC.
- Apply 24 V DC to the converter's power terminals.
- Set the converter's DIL switches for active / passive current loop mode as required by the S5 PLC side (most S5 AS modules are passive).
- Launch STEP 5 in the Windows sandbox and configure the online interface to
S5-AS511at the appropriate COM port.
STEP 5 Sandbox on Windows 7 / 10
On the Field PG M5, STEP 5 is delivered pre-installed in a sandbox environment (a protected virtual OS). The sandbox isolates STEP 5 from the host OS to avoid COM port and registry conflicts. To use the serial port:
- Start the sandbox launcher from the Siemens desktop icon.
- Inside the sandbox, the host COM1 (DB-25 V.24) is mapped to
COM1of the virtual machine. - Configure STEP 5 with:
Interface = COM1,Protocol = AS511,Baud = 9600. - Use
Test → Online → PLC Connectto verify the path to the S5 CPU.
Networked Serial as an Alternative
When the physical COM port is needed for other tasks or the cable run is long, a serial device server such as the Digi PortServer TS can tunnel the V.24 interface over TCP/IP. The STEP 5 sandbox must then be configured with a virtual COM port (e.g., Digi RealPort driver mapping COM10 on the host to the PortServer TS IP address). This approach trades electrical isolation for cable length and routing flexibility.
Verification Checklist
| Check | Expected Result | Tool / Method |
|---|---|---|
| COM1 enumeration in Device Manager | COM1 listed as Siemens COM port (V.24)
|
Windows Device Manager |
| Loopback test pins 2 ↔ 3 | Echoes typed characters in terminal | Tera Term / PuTTY with local echo |
| TTY voltage check on Field PG with S5 option | ~20 mA on pin pair 13/14 when transmitting | Clamp ammeter or breakout |
| STEP 5 online connection to S5 PLC | AG info dialog shows CPU type and version | STEP 5 PLC → Connect
|
| DB-9 adapter continuity | All mapped pins (table above) pass continuity | Multimeter continuity mode |
Troubleshooting Matrix
| Symptom | Likely Root Cause | Corrective Action |
|---|---|---|
| No COM1 visible in host OS | Driver not loaded; check Siemens Field PG driver package | Reinstall driver from the Field PG Tools USB stick |
| STEP 5 cannot find COM1 in sandbox | Sandbox COM mapping disabled | Re-enable COM1 passthrough in sandbox settings |
| PG 710 cable plugged in, no communication | Field PG M5 ordered without S5 option (e.g., 6ES7717-1BB02-0BB4) | Use external V.24/TTY converter; S5 cable direct reuse is not possible |
| Garbled characters at 9600 8N1 | Wrong protocol selected or handshake lines not asserted | Force hardware handshake (RTS/CTS) and re-test |
| Communication works on host, not in STEP 5 sandbox | Sandbox captures COM1 exclusively | Close host terminal applications; check sandbox serial redirect |
| Online connect fails after Windows update | Driver signature rejection | Roll back update; reinstall signed Field PG driver |
Safety and Cabling Notes
- Never connect a TTY cable directly to an RS-232 device without an active converter – the voltage levels can damage the current-loop transceiver.
- Keep V.24 cables under 15 m at 19.2 kbit/s, or under 3 m at 115.2 kbit/s, per EIA-232-E.
- Use shielded cable for TTY runs in cabinet environments; ground the shield at one end only.
- Verify 24 V supply polarity to the Phoenix Contact PSM-ME-RS232/TTY-P before powering up.
- Confirm the Field PG firmware / driver package matches the Windows build (Windows 7 and Windows 10 Field PG M5 versions exist).
FAQ
Does the Siemens Field PG M5 MLFB 6ES7717-1BB02-0BB4 support TTY 20 mA on COM1?
No. This MLFB is ordered without the S5 online interface and without the S5 prommer. COM1 is a pure V.24 (RS-232) DB-25 port. TTY signals are not driven by the mainboard.
Can the S5 programming cable from a PG 710 be reused on a Field PG M5?
Only on Field PG M5 units ordered with the S5 option. On units without the S5 option, including 6ES7717-1BB02-0BB4, the PG 710 cable cannot be reused because the TTY pins are unwired on the mainboard.
Which pins are used for a 3-wire RS-232 link to a Siemens PLC?
Pins 2 (TXD), 3 (RXD), and 7 (signal ground) on the DB-25 connector. With the shipped DB-25 to DB-9 adapter, these map to DB-9 pins 3, 2, and 5 respectively.
What external converter is recommended to add TTY to a V.24-only Field PG?
The Phoenix Contact PSM-ME-RS232/TTY-P (order 2744458) is a widely used active converter that translates V.24 to a 20 mA TTY current loop with 2.5 kV isolation between sides.
How is STEP 5 launched on a modern Field PG M5?
STEP 5 runs inside a pre-installed Windows sandbox environment to isolate legacy COM port and registry access from the host OS. Launch it via the Siemens desktop icon and configure COM1 passthrough in the sandbox settings.