Editing LOGO 0BA7 Weekly Timer from WinCC Flexible HMI

Problem Overview

The Siemens LOGO! 0BA7 generation (front-panel label "LOGO! 8.1", released 2014) exposes the parameters of every function block through the Variable Memory (VM) area only when the engineer enables parameter VM mapping in LOGO! Soft Comfort. The Weekly Timer block is one of the most frequently edited blocks, yet WinCC Flexible on a KTP600 Basic Panel cannot parse its VM bytes into a human-readable HH:MM string. Depending on the I/O field format chosen by the engineer, the operator sees either a raw byte (e.g. 0x14 rendered as the integer 20) or an unfiltered hex value with no obvious meaning.

This article documents two field-proven techniques to read and modify a LOGO! 0BA7 weekly timer from a WinCC Flexible HMI: a hexadecimal I/O field that accepts and displays the raw BCD-encoded bytes as "hhmm", and two symbolic I/O fields driven by text lists that give the operator a familiar hour and minute drop-down. Both rely on the same data layout, the same VM mapping, and the same S7-200 communication driver. The choice between them is a trade-off between engineering simplicity and operator friendliness.

Prerequisites and Compatible Hardware

• LOGO! 0BA7 base module with integrated Ethernet. Common order numbers: 6ED1052-1MD00-0BA7 (LOGO! 8.1 12/24 RCE, relay outputs), 6ED1052-2MD00-0BA7 (LOGO! 8.1 12/24 RCEo, with display), 6ED1052-1FB00-0BA7 (LOGO! 8.1 24 CE, transistor outputs), 6ED1052-1HB00-0BA7 (LOGO! 8.1 230 RCE, mains-powered).
• LOGO! Soft Comfort V8.0 or later for project engineering and firmware update. V8.0 matches the 0BA7 generation; V8.1 / V8.2 / V8.3 are used for the 0BA8 and 0BA9 hardware revisions but remain backward-compatible.
• KTP600 Basic Panel (6AV6 648-0AC11-3AX0 PN variant, or 6AV6 647-0AC11-3AX0 DP variant for MPI/Profibus). TP/Comfort panels running WinCC Comfort in TIA Portal can be substituted, with minor differences in the driver dialog.
• WinCC Flexible 2008 SP5, or TIA Portal V13 SP1 and later with the LOGO! HMI driver option, for HMI engineering.
• Standard Cat5/Cat6 Ethernet cable and a unique IP address per device on the same subnet. The LOGO! 0BA7 ships with IP 192.168.0.1; the KTP600 PN defaults to 192.168.0.10.

LOGO! 0BA7 Weekly Timer Data Layout

The LOGO! 0BA7 VM area spans byte addresses 0 through 849, of which the upper region is reserved for retentive flags, system diagnostics, and function-block parameter mapping. Every enabled block parameter claims a contiguous slice of this area. For a Weekly Timer block with three cams (the maximum count in the 0BA7 generation), the memory layout is:

A single Weekly Timer block therefore claims 15 bytes when all three cams are enabled. A block with only one cam in use still reserves 5 bytes. The start address of this slice is assigned by LOGO! Soft Comfort at compile time and is visible in the "Tools → Parameter VM Mapping" dialog.

BCD is the critical detail. A timer value of 14:30 is stored as the byte 0x14 followed by the byte 0x30, not as the integer values 14 and 30 expressed as plain 8-bit numbers. Reading the same bytes as regular decimal numbers produces 20 (0x14) and 48 (0x30), which is what an unconfigured WinCC I/O field will display and the reason operators observe "20" instead of "14:00".

Enabling Parameter VM Mapping in LOGO! Soft Comfort

1. Open the project in LOGO! Soft Comfort V8.x.
2. Select Tools → Parameter VM Mapping (older builds: File → Properties → VM Mapping). The dialog lists every parameter VM area available to the project.
3. Locate the Weekly Timer block (B001 or whichever block number the tool assigned). Tick the parameter rows for the day mask, the on-time, and the off-time of each cam you want to expose.
4. Note the start address. A fresh project with a single Weekly Timer block placed at block number 1 typically starts at VW0 (VB0 = on-hour, VB1 = on-minute) for the first cam, then VW2 (VB2 = off-hour, VB3 = off-minute), with VB4 holding the day mask. These addresses are project-specific and must be verified in the VM Mapping dialog; do not hard-code addresses from a sample project.
5. Click OK to confirm, then transfer the project to the LOGO! 0BA7 via Ethernet (Online → PC → LOGO!) or via SD card.
6. After transfer, verify on the LOGO! 0BA7 built-in display that the parameter is now visible: navigate to the Weekly Timer block with the cursor keys, edit the time on the front panel, then read VW0/VW2 with WinCC Flexible once the LOGO! returns to RUN.

WinCC Flexible Connection and Tag Configuration

The LOGO! 0BA7 implements an S7-200-compatible subset of the S7 communication protocol on TCP port 102. WinCC Flexible ships with a dedicated SIMATIC S7 200 driver that targets exactly this subset.

1. Open the HMI project in WinCC Flexible 2008 SP5.
2. In the project tree, double-click Connections and add a new connection.
3. Set the parameters as listed below.

   Parameter	Value
   Communication driver	SIMATIC S7 200
   HMI device	KTP600 PN (or the panel in use)
   Connection type	Ethernet
   IP address (LOGO! side)	192.168.0.1 (or the configured address)
   Port	102
   Rack	0
   Slot	1
   TSAP (local)	01.01
   TSAP (partner)	01.00 (LOGO! always uses 01.00)

4. Compile and download the connection to the KTP600.

For the equivalent configuration under TIA Portal V13 SP1 and later, select the LOGO! HMI driver instead of S7-200; the dialog options are identical except that TIA Portal exposes a slightly more verbose name "LOGO! 8". The Siemens FAQ 54997729 ("How do you create a time switch with WinCC flexible?") covers the screen-side configuration of a weekly timer that does not use a real LOGO! at all, and is a useful companion reference for understanding the time switch data layout from a different angle.

Defining Tags in WinCC Flexible

For each VM byte used by the Weekly Timer, create a tag in WinCC Flexible. The tag address must match the VM byte address in the LOGO! Soft Comfort mapping exactly. The following example assumes a Weekly Timer block that starts at VW0.

Important details to verify at this stage:

• The data type must be unsigned BYTE. A signed BYTE interprets 0x80 – 0xFF as negative numbers and will display the day mask incorrectly whenever bit 7 is set.
• The tag must be external (pointing at the LOGO! connection), not internal to the panel. Internal tags live in the panel's own memory and are never written to the LOGO!.
• For editing, enable Write back to PLC on every tag. Without this flag, the panel accepts the value on the screen but discards it as soon as the operator navigates away.
• Set the update cycle to 1 s for monitoring. Faster cycles (100 ms) are supported but do not add value because the LOGO! 0BA7 itself only refreshes the parameter VM area once per program scan.

Reading the Timer — Display Strategies

There are three useful ways to read the on-time byte from a screen.

1. Hexadecimal I/O field. Bind an Output I/O field to WT1_OnHour and set the display format to Hexadecimal with 2 digits. The field renders the raw byte as a two-character hex value. For 14:00 the field reads "14"; for 23:30 the field reads "23" and a second field bound to WT1_OnMinute reads "30".

2. Decimal I/O field with the BCD caveat. Bind an Output I/O field to WT1_OnHour and accept the default decimal display. For 14:00 the field reads "20" (decimal interpretation of 0x14). This is rarely useful in production but is invaluable as a sanity check during commissioning: if the field shows "20" where you expect 14, you have confirmed that the tag is reading the correct byte and the only issue is the display format.

3. Concatenated "hhmm" string. Bind a 4-character hexadecimal I/O field to VW0 (16-bit) and the field reads "1430" for 14:30. This is the most compact representation and the easiest for an engineer to recognise at a glance, but it is not editable from the HMI without further scripting.

Choose the strategy that best fits the operator's workflow. For read-only monitoring, the concatenated "hhmm" approach is the most readable. For combined read and write, use two single-byte hexadecimal I/O fields (one for hour, one for minute).

Writing the Timer — Hexadecimal I/O Field Method

1. On the screen, place an I/O field with mode = Input/Output.
2. Bind it to the WT1_OnHour tag.
3. Open the field's Properties dialog. Under Representation → Display format, choose Hexadecimal with 2 digits.
4. Repeat for WT1_OnMinute, WT1_OffHour, and WT1_OffMinute.
5. Compile and download the HMI project.

From the HMI the operator can now tap each field and enter a value such as 14 for 14 hours, or 30 for 30 minutes. The panel writes the BCD byte 0x14 / 0x30 directly into VM, and the LOGO! 0BA7 (or LOGO! Soft Comfort in online view) displays the time as 14:30.

The hexadecimal I/O field has a useful side effect: it accepts only characters 0–9 and A–F. This means a value of 0x2A is rejected as invalid input, but a value of 0x2F (which is not a valid BCD hour) would still be accepted because hex does not know about BCD constraints. Always validate the entered value by reading the LOGO! display after a write.

Writing the Timer — Text List Drop-Down Method

Hexadecimal entry is fast for an engineer but unfriendly for an operator who expects a 24-hour clock. A second technique uses two text lists in WinCC Flexible: one for hours (entries "00" through "23") and one for minutes (entries "00" through "59"). Each text-list entry stores the value the LOGO! expects at the VM byte — that is, the BCD byte interpreted as an unsigned integer (e.g. the text "14" maps to value 20, the text "23" maps to value 35).

Concretely, for the hour text list:

The minute text list follows the same pattern. The entries for 0–9 are values 0–9; entries for 10–19 are values 16–25; entries for 20–29 are values 32–41; entries for 30–39 are values 48–57; entries for 40–49 are values 64–73; entries for 50–59 are values 80–89. Building the 60-entry list by hand is tedious; the fastest approach is to export an empty text list from WinCC Flexible, fill the cells in a spreadsheet, and re-import.

Steps to build the hour text list in WinCC Flexible:

1. In the project tree, right-click Text Lists and choose Add new.
2. Name the list Hours_BCD and set the list type to Decimal (WinCC accepts BCD values as decimals in this case, because the underlying byte interpretation is identical).
3. For each entry "00" through "23", add a row with the display text in the Text column and the assigned decimal value (0, 1, 2, ..., 9, 16, 17, ..., 35) in the Value column.
4. On the screen, insert a Symbolic I/O field bound to WT1_OnHour. Set the Selection list property to Hours_BCD. The field will render as a drop-down.
5. Build a parallel Minutes_BCD text list and bind it to WT1_OnMinute.

The two symbolic I/O fields now look like two drop-downs. Selecting "14" writes 20 to VB0, which LOGO! reads as BCD hour 14. The on-time is now editable by an operator who has never heard the term "hexadecimal".

Day-Mask Editing and Cam Pair Considerations

The day mask byte is a 7-bit field. The bit assignment in the LOGO! 0BA7 is:

Bind a hexadecimal I/O field to WT1_DayMask (or to whichever byte holds the cam's day mask in your project). The operator types values such as 5 for Monday + Wednesday (bits 0 and 2 set) or 7F for every day of the week. For projects with multiple Weekly Timer blocks, repeat the whole procedure for each block. The VM mapping dialog shows the start address of each block's slice; address the WT2_* tags to the slice that LOGO! Soft Comfort has assigned to the second block. Do not assume that block 2 follows block 1 contiguously in VM; LOGO! Soft Comfort is free to insert padding for alignment or to skip reserved regions.

Verification, Diagnostics, and TIA Portal Migration

After completing the procedure, run the following checks.

1. Read-back check. With the LOGO! 0BA7 in RUN, place the LOGO! Soft Comfort online monitor next to the HMI screen. The on-time value displayed on the LOGO! should match the value displayed on the HMI byte-for-byte.
2. Round-trip check. Edit the on-time from the HMI, then read the LOGO! display and confirm the change. If the LOGO! does not reflect the change, perform a power cycle of the LOGO! to force a parameter refresh (a known limitation on 0BA7 firmware earlier than V1.08.01).
3. Network check. From the engineering station, ping the LOGO! IP address. If the ping fails, the panel will not be able to read or write either.
4. Parameter VM mapping check. In LOGO! Soft Comfort, choose Tools → Parameter VM Mapping → View active mapping. If the Weekly Timer block does not appear, the VM area is not exposed and the panel writes will silently fail.

For a sanity check that is independent of the Siemens documentation, the Snap7 LOGO! 0BA7 / 0BA8 reference documents the S7-200-compatible memory layout of the LOGO!, the supported cam counts, and the byte offsets for every function block. Treat Snap7 contents as a third-party cross-check rather than an authoritative Siemens source.

Troubleshooting matrix for the most common field issues:

Engineers migrating a project from WinCC Flexible 2008 to TIA Portal V13 SP1 or later will find that the same VM byte addresses and the same data types apply. The only changes are: the driver name (LOGO! 8 instead of SIMATIC S7 200), the project tree layout, and the HMI runtime image (Comfort panels instead of Basic panels). The two techniques documented above transfer to TIA Portal with only minor renames in the property dialogs.

Frequently Asked Questions