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Old September 27th, 2004, 03:12 PM   #1
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Siemens S7300 Vs S7400 Addressing

I just had a vendor change his mind on the type of Siemens PLC he wanted to use from an S7-400 to an S7-300.

After printing all of the S7-400 books out and getting the drawings almost done I have to start over...I think...

The S7400 addressing stated that the addressing was obtained by taking the (slot number - 1) x 4. Fore example if I had a digital module in slot 5 that would be (5 -1) x 4 = I16.0 - I16.7 for the address.

Does this also apply for the S7300 or is it different....Until I can get a manual printed anyone know?
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Old September 27th, 2004, 03:26 PM   #2

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Hello Jimdi4;
Siemens uses the same addressing scheme on the S7-300 as on the S7-400; but on most of the CPUs you can modify this system addressing and choose whatever you need. The programming software will block you if you try to use an impossible or already-used address. Just open the properties of any module (in the HardwareConfig editor), select the Addresses tab, remove the System Address checkbox and input the address you select.

Hope this helps,
Daniel Chartier
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Old September 28th, 2004, 03:23 AM   #3
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you can reuse your programs and possibly most of your diagrams.
S7-300 and S7-400 are quite similar.
The adressing that STEP7 makes is just a default suggestion. You can change these as Daniel describes.

The limitations will be (S7-300 compared to S7-400):
Smaller i/o image.
Fewer Merkers, S5Timers, Counters.
Less memory for code and data.
Fewer blocks (FBs, FCs, DBs) can be addressed.
Not so much processing power (longer scan time).

If you dont hit the roof with any of the limitations, you should be able to port programs between S7-300 and S7-400 with no problems.
The exact specifications vary with the selected CPU.

Oh, there is ONE snag when moving from S7-300 to S7-400 (so it doesnt apply to you - but maybe to others):
The S7-400 does not have a relay output card with individually isolated outputs. The only relay output card available for S7-400 has its outputs grouped together 2 and 2.
3 strikes and you're out
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Old September 28th, 2004, 07:42 AM   #4

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Just a small addition to JespersMP's post...

The S7300 series can have the same processing power as the 400 series when it comes to execution speed (scan time), the 318 cpu has the same specifications as the 400 series. It's fairly expensive but a nice option if you have to upgrade a plc.

Failure is not an option
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Old September 28th, 2004, 08:47 AM   #5
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Thanks Everyone for your inputs..
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Old September 30th, 2004, 09:58 AM   #6
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Even though the processing power in the S7-318 is comparable to the 400, don't rely on the rack mounted I/O to be anywhere near the same. The communication bus on a 300 is serial and the 400 is parallel. The 318 can process data on Profibus faster than it's bus mounted I/O.
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