Resolving KTP600 HMI Login Loops and Slow Tag Update Cycles

Overview

The SIMATIC KTP600 Basic color PN (catalog number 6AV6647-0AD11-3AX0 and siblings in the 6AV6647-0xxx family) is a 6-inch basic panel widely used with the SIMATIC S7-1200 1214C and TIA Portal V13/V13 SP1. Two issues consistently surface during commissioning: a "login loop" in which the operator is returned to the calling screen after a successful password entry, and a slow tag refresh that causes the value field to skip rather than ramp. Both are configuration issues in the WinCC project, not hardware faults.

This reference walks through the cause of each symptom, the exact configuration path in TIA Portal V13, the auxiliary settings that frequently trap first-time integrators (login attempt limiter, password reset lockout, update cycle of HMI tags, acquisition mode), and a verification matrix that can be run on the shop floor before signing off a project.

System Context and Versions

Before changing any property, confirm the panel catalog number, the firmware version loaded in the HMI, and the TIA Portal project version. A mismatched image version is the leading cause of attributes appearing to "do nothing" after download.

Problem 1 — Login Returns to the Calling Screen

Symptom

When the operator presses a button protected by an authorization level, the SIMATIC login dialog appears. After a correct user name and password are entered, the dialog closes and the operator is returned to the original screen. The button must be pressed a second time to activate the screen change, the function key, or the tag write that the button was meant to perform.

Root Cause

This is the documented behavior of WinCC TIA Portal: the security check on a button is a one-shot validation against the current user record. After a successful login, control returns to the screen object that requested the check, but the original event that triggered the button (e.g. ActivateScreen, SetBit, TriggerTag) has already been consumed. The user must re-trigger it. There is no built-in "on successful login, fire the original event" hook on the button object itself.

The standard remedy is one of the following patterns:

1. Two-step operator UX: explicitly instruct the operator to log in first, then press the action button. The button's authorization check still gates the action; the loop is intentional and the operator simply re-presses.
2. Project-side login screen: call the login dialog yourself from a screen change or a function key, store the result, and only then navigate. This pattern places the user record in the HMI runtime before any protected object is touched.
3. System function in the user view's "OnLoggedIn" callback: in WinCC TIA Portal V13 the Login user view has a configurable OnLoggedIn / OnLoggedOut event that fires when the runtime user changes. Drive the screen activation from this event to avoid the second press.

Configuring the User Administration on the KTP600

1. In the TIA Portal project tree, expand Devices & Configuration > [KTP600] > Runtime settings > User administration.
2. Click Users and add a new user. Assign a group (e.g. Operator, Supervisor, Administrator).
3. Add the corresponding authorization numbers (1..9) under Authorizations. Each button that should be protected is assigned a number; the user must hold that number in their group.
4. Open the protected button: Properties > Security > Authorization. Uncheck "Allow operator control without authorization" and enter the number that matches the user group.
5. For a function key, open Properties > General > Runtime authorization and select the same number.

Eliminating the Second Press — Login Screen Pattern

For panels that need a true one-click transition after authentication, build a dedicated login screen that uses the system function LogOn (in the "Users" PLT) and the OnLoggedIn event of the user view to drive ActivateScreen with the original target screen stored in a local HMI tag.

1. Create a screen Login that contains a User view object (Toolbar > User view). This object supplies the username/password fields and the OK/Cancel buttons automatically.
2. Configure a string tag PendingTarget (internal HMI tag) that is written by the calling button before it calls ActivateScreen "Login". This stores where to go after authentication.
3. On the OnLoggedIn event of the user view (Configure event > Add function), add a script or system function that reads PendingTarget and calls ActivateScreen "<PendingTarget>" using a name-based activation.
4. On OnLoggedOut, return the operator to the home screen.

This pattern is exactly what the integrator is recalling as having seen in a finished project. It is not a property of the button; it is a screen-level choreography.

Password Lockout and the "Login Attempt Limit" Checkbox

When a user is locked, the panel does not offer a "forgot password" link. The only recovery path is to open the project in TIA Portal, navigate to User administration > Users, and re-enter the password. The new password is then transferred on the next project download or on a panel-side import of the user list (ProSave > HMI Files > Recipe/User Administration).

Problem 2 — Tag Update Cycle is Too Slow

Symptom

The HMI displays a tag value (e.g. a timer, a counter, or a PLC integer) but the value only updates in large steps every several seconds. The display "leaps" instead of ramping.

Root Cause

By default, an HMI tag is acquired with a 1-second update cycle and the cyclic in operation acquisition mode. Three properties combine to determine how often the value is refreshed on the screen:

1. Acquisition mode (Cyclic in operation / Cyclic continuous / On demand) — controls when the runtime polls the PLC.
2. Update cycle (100 ms, 200 ms, 500 ms, 1 s, 2 s, 5 s, 10 s, 1 min, …) — controls the polling interval.
3. Display refresh on the screen object (output field, bar, etc.) — bound to the same tag and inherits the cycle.

If the tag is acquired "On demand", the runtime only reads the tag when it is displayed; the screen must be on and the object must be re-drawn. Combined with the default 1-second cycle, this gives the appearance of a sluggish display.

Tuning Update Cycles in TIA Portal V13

1. Open HMI tags in the project tree, double-click the tag whose display is too slow.
2. In Properties > General, set:
   • Acquisition mode: Cyclic continuous (most reliable; polls the tag in the background even when not on screen)
   • Update cycle: 100 ms for fast timers/counters, 200 ms as a default, 500 ms for trend displays
3. Verify the cycle is not constrained by the PLC's pointer area or by the connection. For a 1:1 PROFINET connection the S7-1200 1214C can sustain 100 ms cycles for a few hundred tags without load. For very large tag counts (1 000+), increase to 200–500 ms.
4. Re-compile the project, download the HMI image, and observe the field.

Tag Acquisition Mode Decision Matrix

Additional Diagnostics for the Update Problem

1. Confirm that the connection to the PLC is online. In the HMI runtime, the status bar (configurable) shows Connected / Disconnected. A "Disconnected" status freezes all cyclic updates.
2. Open the connection in TIA Portal Devices & Networks, check the partner IP and subnet. A wrong subnet mask is the single most common cause of the panel going into repeated connection retries.
3. Check the PLC's protection level. If the CPU is in Read/Write protection with a password that the HMI does not know, the HMI will read zero or the last good value, which the operator perceives as a "frozen" value.
4. Check the tag address in the PLC. The HMI is asking for a non-existent DB or offset, and the PLC returns an error that the HMI silently ignores. Validate the address in the watch table of the PLC.
5. Disable any Job Mailbox or Data Block Pointer areas that are not used. Spurious job mailbox usage can stall cyclic traffic on Basic panels.

Question Marks Not Displaying in Text Fields

The original poster also reports that question marks (and sometimes other ASCII characters) do not render in text I/O fields. The cause is the panel's default text font. The KTP600 Basic ships with a font set that does not always include the full ASCII printable range. The remedy is to assign a font that contains the character, e.g. a TTF embedded in the project.

1. Open the I/O field in the screen editor: Properties > Appearance > Font.
2. Select a font that is bundled with the panel image. Arial and Tahoma are typical candidates that include the question mark glyph.
3. If the question mark appears as a fallback box, embed the font into the project: Project tree > Languages & Resources > Project fonts, add a TTF, and reference it on the I/O field.
4. Re-download the project to the panel and verify the character renders.

Verification and Commissioning Checklist

Troubleshooting Matrix

References for Further Verification

Engineers implementing these fixes should always cross-check the panel-specific manual and the WinCC TIA Portal online help against the project at hand. Authoritative entry points:

• Siemens Industry Online Support: support.industry.siemens.com
• SIMATIC HMI Panels — product family page: SIMATIC HMI Panels overview
• S7-1200 Programmable Controller — system manual entry point: S7-1200 system manual (V4.x)
• TIA Portal V13 SP1 documentation portal: TIA Portal V13 SP1 entry page

FAQ