Communication resumes when PCIN 4.2 addresses the correct PC port and uses its coded baud selection: set /PCOMNumber to 1 for COM1, then set the /PCOM baud-rate row to 4 for 600 Bd. Do not enter the literal number 600 where PCIN expects a selection code.
Serial parameter mechanism
An asynchronous serial link works only when both endpoints use the same baud rate, data framing, and applicable handshaking. Baud rate defines the symbol rate. Data framing defines the data-bit, parity, and stop-bit interpretation applied to each character.
PCIN represents at least some communication choices with numeric codes rather than literal engineering values. For this configuration, baud selection 4 means 600 Bd. The value is an enumeration index, not four baud and not a request to type 600.
A Windows port-properties list that jumps from 300 to 1200 does not by itself settle whether PCIN can request 600 Bd. Configure the rate inside PCIN first. If that request fails, the deciding test is whether the installed serial-port driver and hardware accept the rate when PCIN opens the port.
Check 1: Physical connector and logical interface
The Siemens 880T installation has one 25-pin serial connector but shows four interface-related baud entries: 600 Bd, 110 Bd, 2400 Bd, and 300 Bd. The term interface here means a configurable communication channel or record; it does not necessarily mean a separate physical connector.
| Reading | Meaning | Next action |
|---|---|---|
| One 25-pin connector and several parameter records | The records may represent selectable channels, modes, or logical interfaces sharing hardware. | Identify which record is active for the transfer function, then continue to Check 2. |
Transfer function references the record set to 600 Bd
|
The PC must use 600 Bd. |
Continue to Check 3. |
| Active record cannot be identified | Changing PCIN alone may match the wrong controller record. | Read the interface assignment in the Siemens 880T configuration or its applicable manual before editing values. |
Do not choose the first of four records merely because the connector is physically first or unique. The active record is determined by the control configuration and the data-transfer function.
Check 2: Active Siemens 880T parameter set
Check 2: command a transfer from the control and observe which configured communication channel the transfer function uses. Expect the selected channel to point to the record whose baud setting is 600 Bd if that is the intended machine setting.
If the active channel instead points to 110 Bd, 2400 Bd, or 300 Bd, match PCIN to that active rate or deliberately change the control configuration through the documented Siemens procedure. Do not change several records at once; doing so removes the distinction needed to diagnose channel selection.
The four displayed rates do not identify the data bits, parity, stop bits, or handshake mode. Read those fields from the active Siemens 880T interface record. Record every value before making changes because matching the baud rate alone cannot correct a framing or flow-control mismatch.
Check 3: PCIN port and baud selection
Check 3: open the PCIN 4.2 communication configuration and inspect the command rows. Expect /PCOMNumber to contain the number of the PC serial port and the /PCOM baud-rate row to contain PCIN's coded selection.
| PCIN row | Required value | Interpretation |
|---|---|---|
/PCOMNumber |
1 |
Selects COM1. |
/PCOM baud-rate row |
4 |
Selects 600 Bd. |
If PCIN is configured for another COM-port number, it can open an unused port while the cable remains connected to COM1. The symptom is complete silence even when every framing field is correct. If the port number is 1 and baud selection is 4, continue to Check 4.
If PCIN reports that it cannot open the port, close other applications that may own COM1 and retry. If it opens the port but the driver rejects the rate, test with serial hardware and a driver that expose 600 Bd to PCIN; changing controller framing will not correct a PC-side rate rejection.
Check 4: Framing, handshake, and cable path
Check 4: compare the PCIN framing fields with the active Siemens 880T interface record field by field. Expect identical data-bit, parity, and stop-bit selections. The exact values must come from the control configuration or the applicable PCIN and Siemens documentation; they are not defined by the baud-rate code.
| Symptom | Likely branch | Diagnostic |
|---|---|---|
| No receive activity | Wrong COM port, inactive controller channel, cable signal-path error, or blocked handshake | Confirm port ownership, active channel, conductor continuity, crossed transmit/receive paths, common reference, and required handshake conductors. |
| Characters arrive but are corrupted | Baud or framing mismatch | Recheck /PCOM = 4 and compare data bits, parity, and stop bits. |
| Transfer starts and then stalls | Handshake or receive-flow problem | Compare the flow-control mode at both endpoints and inspect the required control-signal path. |
PCIN cannot open COM1
|
Port conflict, missing port, or driver rejection | Verify the operating system presents COM1 and that no other program has it open. |
A cable assembled to a diagram still requires electrical verification. Check continuity end to end and rule out shorts between adjacent pins. Then verify that the diagram applies to these two endpoint roles; a straight-through cable and a crossed transmit/receive cable are not interchangeable.
Resolving procedure and numbered verification
- Identify the Siemens 880T interface record used by the requested data-input or data-output operation. Expect that record—not merely one of the other three displayed records—to show
600 Bd. - Read and record its data bits, parity, stop bits, and handshake selection. Expect one definite value for every enabled framing and flow-control field.
- Connect the verified 25-pin cable to the machine and the PC serial path assigned as
COM1. Expect continuity on every required conductor and no unintended shorts. - In PCIN 4.2, set
/PCOMNumberto1. Expect PCIN to openCOM1without an in-use or unavailable-port error. - Set the
/PCOMbaud-rate row to4. Expect PCIN to interpret the selection as600 Bd. - Copy the active controller framing and handshake selections into the corresponding PCIN fields. Expect an exact field-by-field match; do not infer stop bits or parity from the baud rate.
- Run a controller-to-PC transfer. Expect PCIN to show receive activity and intelligible, stable data rather than silence or corrupted characters.
- Run a PC-to-controller transfer using a noncritical test file accepted by the control's normal procedure. Expect the control to acknowledge or complete the transfer without stalling.
FAQ
Why does Windows COM1 not list 600 baud?
A general port-properties dialog may expose a different preset list from the communication application. Configure PCIN's baud row as /PCOM = 4; if the port still rejects the request, test the installed serial driver and hardware.
Why does the Siemens 880T show four baud rates with one connector?
The displayed entries can be logical communication records rather than four physical sockets. Identify the record selected by the data-transfer function before deciding which rate PCIN must match.
Why is there no signal after selecting 600 baud?
Baud matching does not correct a wrong COM port, inactive controller record, framing mismatch, blocked handshake, or incorrect signal crossing. Check those branches in that order after setting /PCOMNumber = 1 and /PCOM = 4.
How do I verify the Siemens 880T serial fix?
Perform a controller-to-PC transfer and expect readable data at PCIN, then perform a PC-to-controller test and expect the control to complete or acknowledge the transfer without corrupted characters or a stall.