Siemens 6ES5734-1BD20 Retrofit-Compatible S5 Programming Cable

Siemens 6ES5734-1BD20 Retrofit-Compatible S5 Programming Cable for Legacy System Modernization

The Siemens 6ES5734-1BD20 is an original SIMATIC S5 series programming cable designed to establish a reliable communication link between a PC or programming device (PG) and Siemens S5-series programmable logic controllers. As industrial facilities worldwide continue to operate aging S5 platforms — including the S5-90U, S5-95U, S5-100U, S5-115U, S5-135U, and S5-155U — the 6ES5734-1BD20 remains a critical interface component for program upload, download, online monitoring, and diagnostic access. Whether you are maintaining an existing S5 installation, executing a phased migration to the SIMATIC S7-300 or S7-400 platform, or sourcing a verified replacement for a failed cable, this unit provides the physical and electrical compatibility required for uninterrupted engineering access.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

When planning a retrofit or partial migration of an S5-based control system, the 6ES5734-1BD20 programming cable is typically the first tool required on-site. Before any program backup or logic modification can begin, engineers must establish a stable communication link between the programming device and the CPU module — whether that is a 6ES5095-8MA02 CPU 945, a 6ES5090-8MA01 CPU 090, or a compact controller such as the 6ES5095-8MB01. Without a functioning programming cable, no program upload is possible, and the risk of losing the existing ladder logic or STL program during hardware replacement becomes significant.

In a typical S5 retrofit scenario, the engineering team will use the 6ES5734-1BD20 to first back up all program blocks (OBs, FBs, DBs, and SBs) from the existing CPU to a PC running STEP 5 or a compatible S5-for-Windows environment. This backup is essential before any work begins on the power supply module — such as replacing an aging 6ES5955-3LC41 or 6ES5955-3LF41 PS 955 power supply — or before swapping out I/O modules on the S5 subrack. During this phase, engineers must also document the existing module slot assignments, I/O addresses, and any analog signal ranges configured on modules such as the 6ES5464-8MA11 analog input module or the 6ES5470-8MA12 analog output module, as these parameters must be replicated or remapped in the replacement hardware.

For facilities transitioning from S5 to S7, the 6ES5734-1BD20 remains relevant during the parallel-run phase. The S5 system continues to operate while the new SIMATIC S7-300 rack — populated with modules such as the SM 321 digital input, SM 322 digital output, and CP 343-1 Ethernet communication processor — is commissioned alongside it. During this period, the programming cable provides continued access to the S5 CPU for monitoring and comparison of I/O states, ensuring that the new S7 program logic produces identical outputs before the final cutover. Signal isolators and terminal adapters are often required to bridge the wiring between the old S5 I/O terminal blocks and the new S7 front connectors, and the 6ES5734-1BD20 supports the diagnostic work needed to verify signal integrity at each stage.

In control cabinet upgrade projects, available installation space is a frequent constraint. The S5 subrack and its associated 6ES5700-series bus modules occupy fixed DIN rail or panel positions, and the programming cable must be routed without interfering with existing cable ducts or terminal strips. Engineers should confirm that the PG port on the CPU faceplate is accessible before the cabinet is closed, and that the cable length is sufficient to reach the nearest available USB-to-serial adapter or dedicated programming device. For remote or unmanned substations, some teams install a permanently connected serial port extender to allow remote STEP 5 access without opening the cabinet door.

Downtime Control During System Migration

Minimizing unplanned downtime is the primary concern in any S5 retrofit project. The 6ES5734-1BD20 supports this goal by enabling a complete program backup before any hardware is disturbed. Once the backup is confirmed and verified — by comparing block checksums or performing a test download to a spare CPU — the physical replacement work can proceed with confidence that the program logic is preserved and recoverable.

To protect the original program logic during migration, engineers should store the STEP 5 project file in at least two independent locations (local PC and network share or USB drive) before beginning any hardware removal. If the existing CPU is being replaced with a same-generation spare — for example, substituting a failed 6ES5095-8MA02 with a tested replacement unit — the 6ES5734-1BD20 is used immediately after installation to download the backed-up program and verify online status. If the migration involves a cross-generation upgrade to S7, the STEP 5 project can be imported into STEP 7 using Siemens’ conversion utilities, though manual review of all program blocks is strongly recommended to catch any S5-specific instructions that do not have direct S7 equivalents.

Field continuity during migration is maintained by keeping the S5 system in RUN mode for as long as possible, switching to STOP only during the final I/O rewiring phase. The programming cable allows the engineer to monitor the S5 CPU’s diagnostic buffer and I/O status in real time, providing early warning of any faults introduced during the rewiring process. Once the new system is confirmed to be operating correctly, the S5 CPU can be placed in STOP and the old subrack de-energized. Total controlled downtime for a well-prepared S5 CPU replacement using this workflow is typically two to four hours, depending on the complexity of the I/O wiring and the number of program blocks involved.

Retrofit Support FAQ

Q1: Is the 6ES5734-1BD20 a direct replacement for other S5 programming cables?
Yes. The 6ES5734-1BD20 is the standard TTY/RS-232 programming cable for the SIMATIC S5 series and is compatible with all S5 CPUs that feature a PG port. It replaces earlier cable variants used with the same controller family. If your existing cable has a different suffix (e.g., 6ES5734-1BD00), verify the connector type on your CPU faceplate before ordering, as minor interface variations exist across S5 sub-series.

Q2: What commissioning steps are required after connecting the 6ES5734-1BD20?
After physically connecting the cable, open STEP 5 or S5 for Windows and navigate to the interface settings. Select the correct COM port (typically COM1 or COM2 on older PCs, or the virtual COM port assigned by your USB-to-serial adapter driver). Set the baud rate to match the CPU’s PG port configuration — 9600 baud is standard for most S5 CPUs. Perform an online connection test before attempting any program upload or download.

Q3: Can this cable be used during a live S5-to-S7 migration without interrupting production?
Yes, provided the S5 CPU remains in RUN mode. The 6ES5734-1BD20 supports online monitoring and program upload without forcing the CPU into STOP. This allows engineers to back up the existing program and monitor I/O states while the production line continues to operate. Only the final download and I/O rewiring phases require a controlled STOP.

Q4: What are the stock availability and warranty terms?
The 6ES5734-1BD20 is available from stock at NINERMAS. All units are tested prior to shipment and covered by a 12-month warranty against manufacturing defects and functional failure. Expedited shipping is available for urgent retrofit and breakdown recovery requirements. Contact our team for lead time confirmation and volume pricing.