FB120 carries the orange half-circle in the project tree and the block you have open is the one you wrote on Tuesday. On an S7-1500 that symbol is the result of a checksum comparison, not a time stamp comparison, and the manual lists more than a dozen separate checksums behind it. Three of them have … Read more
The batch record says the mixer started at 06:14 and the operator watched it start at 07:14, on the Sunday the clocks moved. The CPU 1516-3 PN/DP is keeping perfect time. What is wrong is that somebody wired RD_SYS_T into the timestamp and RD_SYS_T hands back the module time, which on this family is always … Read more
MOVE_BLK with COUNT := 20 aimed at an ARRAY[1..10] of Real on a CPU 1516-3 PN/DP does not put the CPU in STOP and does not hand you an error in the diagnostics buffer. The enable output drops to 0, and on a box inserted with the editor’s default settings there is no ENO pin … Read more
BadIdentityTokenRejected is the answer an OPC UA server gives when the secure channel is up, the client certificate is trusted, and the session request arrives with no user in it, and on an S7-1500 with guest authentication off that is exactly where a first Python OPC UA client stops. It is the third of four … Read more
A snap7 S7-1200 read – plc.db_read(12, 0, 12) against a CPU 1214C – returns twelve bytes on the bench and an exception on the machine, and the difference is two checkboxes in TIA Portal, neither of them on the Pi. python-snap7 3.1.2 talks the S7 protocol to TCP port 102 in pure Python, so there … Read more
On an S7-1200 or an S7-1500 there are four places a function block can keep state that is not in its instance DB, and every one of them makes a second FB instance of FB_Valve share memory with the first. The report is always one of three: valve 2 opens when valve 1 is commanded, … Read more
An optimized block on an S7-1500, or on an S7-1200 at V4.x, is created with a 100 byte memory reserve, which is room for 25 Reals of new Statics before a download in RUN has to reinitialise the instance DB. Whether an S7-1500 interface change makes the load preview put “reinitialize” against the block is … Read more
A GET on a CPU 1511 that reads from a CPU 1214C and comes back with ERROR = 1 and STATUS = 8 has almost always been refused by the 1214C, and the 1214C has no code in it to blame. Two settings on the partner decide whether PUT and GET ever return data, and … Read more
Siemens gives you a Retain checkbox and a published memory budget. Rockwell gives you neither. Here is what each one really keeps, and how to check it.
Monitor a block on an S7-1500, build a watch table, and work out why a value sits there: modify against force, optimised blocks, and what STOP does.
Start search comes back empty on an S7-1200. Work through the PG/PC interface, the subnet, the flash-LED check and a CPU that loads but stays in STOP.
The station is an IM 155-6 PN with an ET 200SP F-DI 8x24VDC HF in slot 3, the CPU is a 1515F-2 PN on TIA Portal V17, and the hardware compiles clean with a warning that says the F-module has no valid PROFIsafe address yet. The guard door on channel 2 is wired as two … Read more