Monitor a legacy PLC program when the source is gone

What you need

• Cable. D2-DSCBL, the DL205 programming cable: 12 ft long, shielded, with a 9-pin female D-sub on the computer end.
• Software. DirectSOFT, the maker's programming package, bought or downloaded from AutomationDirect or its distributor. The maker has also published a free version of the same package with a program-size limit, so a program larger than that limit will not display in full.
• Converter. A USB-to-serial converter when the computer has no 9-pin serial port. Adapter compatibility is the usual failure point with PLC software; the converter the maker sells for its own software is the choice that removes it.
• Reach. The cable is 12 ft, so the computer sits within 12 ft of the rack for the session. A longer run needs the distances in the serial-cable article linked below.

Match the cable to the CPU port

Read the model off the CPU nameplate before ordering anything. AutomationDirect's cable table lists, for each CPU, which port takes the programming cable; on DL205 CPUs the D2-DSCBL lands on the top port in the CPU. Where a top port is a 15-pin connector, the same table calls for the maker's RS232 data communications unit between cable and CPU, so the nameplate and the table decide the parts list. Serial cables that look alike are wired differently, and the part number is the only match to trust.

Connect and monitor, step by step

1. Install the DirectSOFT release that runs on the PC's Windows version. If the only copy you can find is an old release built for Windows XP, the documented compatibility route is in running legacy HMI programming software in XP compatibility mode.
2. Connect the chain: converter into the PC, D2-DSCBL into the converter's 9-pin port, cable into the CPU's top port. The CPU keeps running its scan while you plug in; a serial connection changes nothing in the program.
3. Note the COM port Windows gave the converter and select it in the software's link setup. If the software's port list stops at COM4 while the converter sits above it, remapping a USB serial adapter when software lists COM1 to COM4 names the fix.
4. Go online. Check the CPU identification the software reports against the nameplate; a mismatch means the cable is on the wrong port or the wrong CPU.
5. Watch the ladder. Contact and coil states move live as the machine cycles, and you change nothing.

How to check it worked

The link is good when bits toggle on screen while the machine cycles. The software manual documents the Online toolbar with two transfer buttons: Read PLC brings the program from the CPU to the PC, and Write PLC sends the open program from the PC to the CPU. A monitoring session runs neither. Write down the CPU model, the software release, the converter and COM port, and any message the software showed; that list separates a repeatable communication fault from a locked program if support is needed later.

Read the program back out

If the ladder opened with no password prompt, the lost source is recoverable on the spot. Select Read PLC on the Online toolbar and the software pulls the program from the CPU into a file on the PC. Save that file twice, one copy off site; the recreated file is the replacement source for the program nobody has. Keep Write PLC out of the job: a write sends whatever is open in the software into the CPU and can alter or erase logic a running machine depends on. Never test a link with a program transfer; watch live bits, and transfer only when you mean to keep the file.

If the program asks for a password

When the software goes online and then asks for a password before the ladder appears, the program is locked in the CPU. No software setting, cable swap or converter change removes a program password. The documented path is the manufacturer's service: send the CPU to AutomationDirect's service department, which applies the factory recovery procedure for that product. The machine keeps running on the program it holds; the lock blocks access from the software, so the plant loses the CPU only when you ship it. Open the ticket before you pull the unit.

Example: rebuild a lost source from a DL205 rack

Scenario: a plant inherits a DL205 rack with no disks, no printouts and no software. The nameplate goes to the cable table: D2-DSCBL covers the CPU, and the programming port is the top port. The nearest bench spot sits 8 ft from the panel door and the open door needs a 2 ft service loop, so the run is 8 ft + 2 ft = 10 ft; the 12 ft cable reaches with 2 ft spare. The laptop has no serial port, so the converter supplies the 9-pin port the cable's female D-sub mates with. Install DirectSOFT, select the converter's COM port, and go online: the software reports the CPU type and draws a live ladder with no password prompt. Select Read PLC, save the file in two places, and the source exists again. Parts: one cable, one converter.

If the link fails

• No ports listed. The converter's driver did not load; reinstall it and confirm the port in Windows before touching the software.
• Online attempt times out. The software is on the wrong COM port or the cable is on a port that is not the programming port; move the cable to the CPU's top port and recheck the COM selection. Recurring converter timeouts are covered in USB serial adapter timeouts when programming a text panel.
• CPU found, ladder will not open. A password lock; use the service path above.
• Rack beyond the cable's reach. How far an HMI to PLC serial cable runs, by interface lists the distance each serial interface supports, and that decides between moving a laptop and extending the run.

The decision

Recommendation: Read the CPU model off its nameplate and order the maker's cable and converter together so the parts arrive as a matched set. Go online, watch the live ladder, and select Read PLC once you can see it; the file it recreates is your source, saved in two places. If a password prompt appears instead, send the CPU to the maker's service for the documented factory recovery and schedule the downtime before you pull it from the rack.

Questions