Hello,

in my opinion pls check your test again visually, you mix up data types and therefore you can be confused. Simply, if you define on your fx5 data type of buffer as WORD, why you set in S7 data type to INT? I see your display format set as you preffer, but mix up data types I see as not good idea, simply you can have chaos in values. In any case, if you take simple calculator and check values received (dec value) and convert it to hex, you can simply see that you received right changed values from your Fx5 PLC, so info that you not received data (NDR isn't true) is false. Output statuses from your TRCV block are available for one scan cycle som you need prepare conditions to catch them, not visually check, but let return to primary problem. Due S7-1200 CPU and firmware versions also instruction can be different. What is exactly your S7 order number and firmware version? What Automation SW (SP, Update) you're using? All is important to know, also in TIA help is all described what you need set in input parameters correctly due your requirements, also what you need check in outputs of block - ERROR, STATUS,... Again to base of problem, your DATA input parameters point to your recv buffer, but only to first element of array - [0]. You need change this to whole buffer, so if you'll set this click on end to none not to [0] element. This is first primary problem. Make tests and return with infos.

Hello,

ok, but this is probably known from TCP protocol basic functionality as stream protocol not as directly Siemens problem so programmer has more options how to receive messages with some defined criteria. Using predefined end detection characters, send first one/two bytes as info about next send amount of data or set AdHoc dynamic length receive option. In case of AdHoc option I've asked you about version of your S7-1200 and firmware, look again to my post. With versions some other blocks exists with different AdHoc implementation, therefore you need to know what HW you have in your prj. All is documented in help, also system of dynamic receive message length exists for S7-300 (look here in Forum for this), but implementation in S7-1200/1500 looks to me better now in my opinion. Also in this case you don't need implement 10x filling your buffer to reach 100 byte full, you can also define 10 bytes long buffer if your messages are same in length or implement mentioned solutions. This working without problems.

Update: here it is (link): S7-300 Dynamic recv length Example