The Koyo SZ-4 is the same CPU as the D2-240 in the DL205 line, and DirectSOFT supports it. Create a fresh project with PLC type D2-240, wire a cable that matches the SZ-4's own port, and set the link to that port's speed: Port 1 runs a fixed 9.6 kbaud, Port 2 spans 300 baud to 19.2 kbaud. Upload and back up the program before you download anything.
The SZ-4 on that base is not a mystery. It is the D2-240 of the DL205 family, sold under the Koyo name, and DirectSOFT supports it. That one fact decides the whole job: create the project as a D2-240, use a cable cut for the SZ-4's own ports, and set the link to the port you actually plugged into. A project written for a DL260 and the cable that serves it do not carry over, because the DL260 is a larger CPU in the same family, with more memory, more instructions and its own port set. Work through the steps in order. Each one ends with a check that has to pass before you move on.
Program it as a D2-240, not a DL260
AutomationDirect publishes a PLC cross-reference on its support site that maps the SZ-4 marking to the D2-240 and lists it as DirectSOFT-supported. The PLC type you pick in DirectSOFT is what the software validates your logic against: memory ranges, instruction set, port behavior. Pick DL260 for an SZ-4 and you get a rejected download, a link that times out, or a project compiled for hardware that is not in the panel.
Read the marking on the CPU, find that marking in the cross-reference, and let the row pick the PLC type.
Check: the row for your marking names the D2-240. If the marking is not listed, stop there and take the marking to the PLC maker's support before anything is written to the CPU.
What you need
- DirectSOFT, installed from the PLC maker's own support site so the version and license match. DirectSOFT5 already covered the DL205 family, including this CPU.
- A serial cable that matches the SZ-4 port you will use: Port 1 for online edits, Port 2 for program transfers.
- A USB serial adapter if the PC has no COM port.
- The DL205 user manual, for the port connector wiring.
- The part number of every module seated on the base.
| Port on the SZ-4 | Speed | Use it for |
|---|---|---|
| Port 1 | fixed 9.6 kbaud | small online edits |
| Port 2 | 300 baud to 19.2 kbaud | set 19.2 kbaud for uploads and downloads |
If the PC will sit far from the panel, check the distance limits first. Serial interfaces have very different reach, and the numbers per interface are in HMI to PLC serial cable maximum distance by interface.
Build the project and the link
- Confirm the CPU. Read the marking on the module and find it in the vendor's cross-reference. The SZ-4 row maps to the D2-240.
- Create a new project with the PLC family set to D2-240. DirectSOFT then starts a fresh .dsproj built for that CPU. Do not copy the DL260 project and edit it; port its logic later, if you need it at all.
- Wire the cable to the port you chose and match it to the DL205 manual's connector wiring for that port: transmit, receive, ground. If a connector does not seat, stop. Do not force it and do not rewire a cable from memory; a DL260 cable is cut for a different port set.
- Create the link. Select the COM port your adapter enumerates as (Device Manager confirms the number on a USB adapter), set the PLC type to D2-240, and set baud, parity and station address to that port's own configuration. Do not reuse the DL260 link's values.
- Run the link test. A timeout leaves three suspects, in this order: wrong COM port, wrong serial settings, wrong cable wiring. Change one at a time.
- Go online and read the PLC information. The CPU must report as a D2-240. Then upload the program into a new project and save it under a dated name before you touch any logic. That upload is your backup, the same discipline as reading an HMI project from the panel before editing it.
- Compare the uploaded logic with any archived source you hold and resolve differences before changing anything. If no archive exists, monitoring a legacy PLC program when the source is gone covers what you can still do from the running CPU.
- If you port DL260 logic into the D2-240 project, move it function by function and prove each one on the CPU. The habit from opening an old HMI project in new software and converting it safely applies here too: a converted project earns trust only after it has run.
- Download only when you must, only from the D2-240 project, and only with the outputs in a safe condition. A download to a running machine can move outputs no one is watching.
Example: a full 32 KB backup over Port 2 at 19.2 kbaud
Inputs, and where each comes from:
- Program size: 32 K byte, the size of the D2-EE-2 EEPROM cartridge the DL205 parts list gives for this CPU. That is 32,768 bytes, and it is the largest image you would pull.
- Line speed: 19.2 kbaud on Port 2, the top of that port's documented 300 baud to 19.2 kbaud range, so 19,200 bits per second.
- Framing: one start bit, eight data bits, one stop bit, no parity, which is 10 bits to carry each byte. Parity switched on adds an eleventh.
Rule in words: bits per second on the line, divided by bits per byte, gives bytes per second. Program bytes, divided by bytes per second, gives seconds of line time.
Arithmetic:
- 19,200 / 10 = 1,920 bytes per second.
- 32,768 / 1,920 = 17 s.
- With parity: 19,200 / 11 = 1,745 bytes per second, and 32,768 / 1,745 = 19 s.
Result: 17 to 19 seconds of pure line time for the full 32 K byte image.
What moves it: Port 1 is fixed at 9.6 kbaud, so 9,600 / 10 = 960 bytes per second and 32,768 / 960 = 34 s, twice the Port 2 time. A Port 2 left at 1,200 baud moves the same image in 1,200 / 10 = 120 bytes per second, and 32,768 / 120 = 273 s, about 4 minutes 33 s. Protocol overhead and retries add on top, so the real transfer runs longer than the line-time figure.
Decision: set Port 2 to 19.2 kbaud for full uploads and downloads. A backup that takes minutes means the link is running at a low baud or retransmitting; fix the link before you trust what it copied.
Check every module on the base
The base looks like DL205 hardware because it is DL205 hardware, so confirm the modules by their own part numbers, one at a time. Write down the part number and slot position for every seated module; on a nine-slot base such as the D2-09B-1 that is nine numbers. Check each against the DL205 module documentation and the D2-240's documentation. Any module with no documented match is unverified: give it a note and keep it out of the replacement plan until it resolves.
Check: every populated slot ends the job with either a documented match or a note and an owner.
How you know it worked
- The link test completes and reports the CPU.
- The online PLC information reads D2-240.
- A dated backup project sits on the PC and its logic matches the CPU.
- Every populated slot shows live points that agree with the field devices.
- If the panel carries a D2-EE-2 cartridge, it holds the current program.
Recommendation: Build every SZ-4 project fresh with PLC type D2-240, run full uploads and downloads on Port 2 at 19.2 kbaud, leave small online edits on Port 1 at its fixed 9.6 kbaud, and pull a dated backup before any download. If you also service a DL260, label a separate cable and link for each CPU so the DL260 pair never lands on the SZ-4.
Once the CPU is documented and backed up, the operator-facing side of the cell, andon boards and notice screens included, is a separate job, and that is the one our shop-floor screens and andon boards are built for.
Questions
Can I back up the SZ-4 program without a PC?
The DL205 parts list includes the D2-EE-2 EEPROM cartridge for this CPU, sized at 32 K byte. The cartridge keeps a copy of the program in the panel, so a replacement CPU can be brought up without pulling the logic over the serial link first. Keep the dated PC backup as the master copy and refresh the cartridge whenever an accepted change goes in.
The CPU carries a password from a previous owner. What is the path?
Use the PLC maker's documented recovery, which starts at their technical support with proof of ownership. Do not rewire, short or substitute hardware to get around a password: an undocumented workaround on a CPU you cannot yet read puts a machine you know nothing about at risk. Until the password is resolved, keep any link read-only and change nothing in the panel.
Which DirectSOFT release runs the SZ-4?
The vendor's cross-reference lists the SZ-4, mapped as the D2-240, among the CPUs DirectSOFT supports, and DirectSOFT5 already covered the DL205 family. Take the installer from the PLC maker's own support site so the version and license match your CPU, and note the release number with the project file, because a project reopened in a different release should be re-verified before you trust it.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.