Resolving LOGO! 8 VM Mapping Asynchronous Timer TH Value Error

Problem Overview

When a Siemens LOGO! 8 Base Module (order suffix 0BA7 and later) is configured with an extended web server page through the LOGO! Web Editor (LWE), operator-entered time values appear to be mis-scaled when written to the asynchronous pulse generator's TH (high-time) parameter through Variable Memory (VM) mapping. A typical symptom: an operator types 1 min on the web page, but the asynchronous timer block reports 5:00 on the TH parameter, or vice versa. The fault does not originate in the LOGO! firmware or in the asynchronous timer block itself — it is produced by the wrong scaling function being inserted in the LWE project between the HTML input widget and the VM target.

The mapping type in the user's project is VB-4 Hex writable (a four-byte, hexadecimal, write-enabled Variable Byte). The address in VM is a 32-bit slot that the LOGO!Soft Comfort project uses to expose the timer's TH word. The two legitimate ways to expose TH to the web page are the Analog value function and the Scale Time function. They are not interchangeable; mixing them produces a 5× (or other rational) drift of the displayed time against the stored value.

Root Cause: Wrong Scaling Function in the LWE Project

The asynchronous pulse generator (block symbol on the LOGO! editor) has a TH input that expects a time value expressed in the time base you selected in the block's properties dialog — the available bases are 10 ms, 100 ms, 1 s, and 1 min. The raw word stored in VM is therefore an integer count in the chosen base, not an engineering time in seconds or minutes.

LWE supports two scaling primitives that look superficially similar but have very different semantics:

• Analog value (linear scaling) — applies a linear transformation Display = a·Raw + b. Suitable for measured variables such as temperature or pressure where the raw word and the display unit share a fixed engineering scale.
• Scale Time (time-base aware scaling) — applies the LOGO!-native conversion between the time base chosen in the block properties and the engineering unit used on the web page. This is the only correct primitive for TH / TL of any time block.

If the project uses Analog value with a span configured in minutes (for example, raw 0…5 mapped to display 0…1 min), the web page textbox will indeed show 1.00 when the operator types 1, but the raw word the operator just typed is interpreted as a unitless count, not as a minute. The asynchronous timer block, configured with a time base of 1 min, therefore evaluates the raw count of 5 as 5 minutes — which is exactly the 5:00 the user observed.

LOGO! VM Mapping Architecture (0BA7 and Later)

Per the official Siemens support article 100782807 — Parameter VM Mapping (0BA7 and later versions only), the LOGO! Base Module exposes selected function-block parameters to a 32-bit-wide Virtual Memory (VM) area. Key constraints:

• Maximum of 64 parameters per Base Module can be mapped in the Variable Memory Configuration dialog of LOGO!Soft Comfort.
• Each VM slot is 32 bits wide; LOGO!Soft Comfort addresses it with the four-byte notation VB-4 (or, equivalently, as a 16-bit word at the same starting address with VW).
• Mapping mode is configured in the dialog as read-only, write-only, or read/write. The user's VB-4 Hex writable selection maps directly to the write mode with hexadecimal display.
• Mapping applies to the LOGO! 8 series only; LOGO! 6 (0BA6) does not have a comparable VM-mapping capability.

Why a Hex Slot Is Risky for a Time Parameter

A time value is conceptually a non-negative integer in a fixed base. Storing it in a hex-display slot is technically legal (it just means the LWE page will format the number with 0x), but it removes the implicit reminder that the variable is a count. If the operator types 1 in the LWE input, the value written to the VM is the raw count 0x0001. The asynchronous timer interprets this as 1 unit in the configured time base, producing the 5× drift described above only when the Analog-value scaling has been configured with a span of 0…5 instead of 0…1.

Solution: Replace the Analog Value Function With Scale Time

The fix is to swap the linear Analog value primitive in the LWE project for the Scale Time primitive, then re-deploy the project to the LOGO! Base Module.

Prerequisites

• LOGO!Soft Comfort V8.0 or later, with the LOGO! Web Editor V1.1.0 add-on installed. Older LWE builds do not contain the Scale Time primitive in compatible form; if you must open a project created in an older LWE, you must first upgrade the LWE project, but note that downgrading after upgrade is not possible.
• Administrative access to the LOGO! Base Module (admin password) so that a new circuit program can be transferred.
• Ethernet connectivity between the programming PC and the LOGO! Base Module on the same subnet.
• A backup of the existing LSCZ/LWE project file.

Step-by-Step Procedure

1. Back up the project. Save a copy of the existing .lsc and LWE project to a separate folder before editing.
2. Update LOGO! Web Editor. If your LWE installation is older than 1.1.0, install the current build. Open the LWE project, accept the upgrade prompt, and save the upgraded project under a new name so the original remains recoverable.
3. Open the web page in the LWE editor and locate the input widget bound to the TH variable (the field currently mapped to a 32-bit hex slot, e.g. VB-4 Hex writable).
4. Remove the Analog value scaling element sitting between the input widget and the VM binding.
5. Insert a Scale Time element from the LWE toolbox. Configure it as follows:

   Field	Setting
   Time base	Match the asynchronous timer block's time base (10 ms / 100 ms / 1 s / 1 min). The most common choice for a long pulse is 1 min.
   Input type	Signed integer (the timer's TH is non-negative, but LOGO!Soft Comfort's VM slot is signed 32-bit).
   Output engineering unit	Same unit as the time base (min if base is 1 min).
   Display format on web page	mm:ss or h:mm per HMI convention.

6. Re-bind the input widget to the VM slot, but select VB-4 Decimal writable instead of Hex. Decimal display is the default for time parameters; a hex slot on a time parameter is a strong indicator the project was misconfigured.
7. Compile and transfer the LOGO! circuit program to the Base Module, then publish the updated web project through LWE.
8. Cycle power on the LOGO! Base Module to ensure the new VM mapping table is loaded; the LOGO! 8 family does not always re-evaluate the mapping table on a soft restart.

Verification

After deployment, validate the fix end-to-end with the following checks.

1. Browser-side check. Open the extended web page in a browser pointed at the LOGO! Base Module's IP address on port 80 (HTTP) or 443 (HTTPS, if enabled). Type 1 min in the TH input field, click Set, then refresh the page. The displayed TH value on the web page must read 1:00 (or 01:00 in mm:ss format), and the underlying value in the LOGO! display/TDE must show 00:01m.
2. LOGO! display check. On the LOGO! Base Module's integrated display (or the connected LOGO! TDE), navigate to the asynchronous timer block. The TH parameter must report the time in the selected base — e.g. 00:01m for one minute.
3. Run-time check. Trigger the timer and observe the output for at least three full periods. The output must remain high for exactly the TH duration and remain low for exactly the TL duration.
4. Edge-case check. Enter 0, 1, 59, and the maximum legal value (65535 for a 16-bit time base, or 32767 for signed-16). Each must round-trip without overflow.
5. Network capture check (optional). With Wireshark on the management PC, capture a write to the LOGO! web server and confirm the raw VM word matches the time-base count, not a scaled engineering value.

Parameter Reference

The following table summarises the values that appear in a correctly-configured LWE project for an asynchronous timer with a one-minute time base.

Common VM Mapping Pitfalls and How to Avoid Them

Related Time Blocks That Use the Same Pattern

The same Scale Time primitive is required for every time-domain block in the LOGO! 8 library, not only the asynchronous pulse generator. The following blocks all have TH / TL (or single T) parameters that must be exposed to the web server with Scale Time:

• On-delay timer
• Off-delay timer
• On/off delay
• Retentive on-delay
• Wiping relay (pulse output)
• Edge-triggered wiping relay
• Symmetrical pulse generator
• Asynchronous pulse generator
• Stairway lighting switch
• Multiple-function switch

If you are standardising LWE projects across a fleet of LOGO! Base Modules, define a single web-page template that uses Scale Time for all time parameters; this eliminates the 1×n class of scaling errors entirely.

Migration Notes for Sites Upgrading From LWE < 1.1.0

Several older LWE builds shipped without the current Scale Time primitive, and projects saved in those builds are silently incompatible with newer installations. When a project is opened in a newer LWE the editor offers to upgrade; once accepted, the project can no longer be opened in the older build. Field-engineering practice:

1. Maintain parallel branches: one for the legacy LWE build, one for the current build.
2. Re-author the LWE portion only when the Base Module firmware is upgraded in lockstep.
3. Always re-test the full VM mapping table (all 64 slots) after an LWE upgrade; even unchanged slots can shift address if the tool reorders the table.

Standards and Reference Material

The VM-mapping capability is a LOGO! 8 feature, not a standards-track protocol. For further reading on the underlying web-server model, the official Siemens documentation hub at Siemens Industry Online Support provides application examples for the LOGO! 8 web server. The specific article governing parameter VM mapping is the Siemens support entry 100782807 — Parameter VM Mapping (0BA7 and later versions only).