The cheapest way to achieve Modbus RTU with an S7-300 processor ?

Jeff23spl · Jan 10, 2012

Hello

I even did some Modbus RTU connection using a 315 pn/DP processor, CP341 card and Modbus chip but now i have to use a 300 processor because the projet i try to do, doesn't fit in an S7-200...

The serial port of a 200 is a low cost option but when it comes time to use 300 platform ....outch!

I wonder if there is a way with an ET200S to do Modbus RTU as it include a 314 plc?

I will need at least a 314 processor to handle the math functions i do need....

My last option would be to use a small s7-212 connected to a 277 profibus as a gateway for modbus RTU from the 300 DP master port but...

Mike_RH · Jan 10, 2012

How about using a s7-1200?
It has instructions for Modbus master or slave.
It is inexpensive, as is the rs485/232 modules.
Then it could be an io device to a Profinet master.

KalleOlsen · Jan 10, 2012

Hi!

The Vipa300 CPUs (S7300 clone) has Modbus RTU option on the Profi interface. I have used it, works well. One of the Vipa 314 (don't remember the complete number now) is very cheap also, and very performant, but has little RAM (can be easily extended with a Vipa SD). Check at www.vipa.de

Kalle

Edit:
Must have been this:

Vipa314-2BG03
CPU 314SE/DPS - SPEED7 technology
DC 24V, 128kByte work memory expandable up to 512kByte
(50% program/50% data), MPI, MMC slot, real-time clock
• Interface:
Profi bus DP slave, 12Mbit/s, 1…125/PtP RS485, potential separated,
ASCII, STX/ETX, 3964R, Modbus master, USS master
Ethernet interface RJ45 for PU/OP communication

KalleOlsen · Jan 10, 2012

Here is another 300 clone that talks Modbus RTU and TCP. I think it is quite cheap. (Have never touched it.)

http://www.insevis.de/en/products/compact-plc

Kalle

Pudden · Jan 11, 2012

Hi,

One option is to use a gateway, Profibus Slave to Modbus RTU (master?).
I work for HMS and we make the Anybus Communicator for Profibus - Profibus slave to Modbus RTU master;
http://www.anybus.com/support/support.asp?PID=104&ProductType=Anybus Communicator
If you need to use Modbus RTU over RS232, max.15m, a gateway is probably your only option, as the gateway can be installed close to the modbus slave and use Profibus between the gateway and PLC.

The gateway solution is a very cost-effective solution, compared to CP341....

//Patrick L @ HMS

Bratt · Jan 11, 2012

Modbus library using regular Siemens hardware from runmode.com

Jeff23spl · Jan 11, 2012

Bratt said:
Modbus library using regular Siemens hardware from runmode.com

sounds good have you tried them ?

as i see, there is a few code block pre-made that just need configuration ? sound easy and inexpensive !!!

Mike_RH · Jan 12, 2012

Jeff,
Your definition of inexpensive is different than mine!

Have you looked at a s7-1200 based solution?

Lare · Jan 13, 2012

ET200S can be modbus slave or master with interface module

Homer_BL · Jan 13, 2012

Agree with Mike, S7-1200
or
one S7-222 (modbus master) with Profibus module to be a S7-300 slave.

Cheeper than use of S7-300 as Modbus master.

Pudden · Jan 16, 2012

I still think that cheapest way to get a Modbus master into a S7-300 is to use a gateway...

Jeff23spl · Jan 17, 2012

Mike_RH said:
Jeff,
Your definition of inexpensive is different than mine!

Have you looked at a s7-1200 based solution?

My definition is something safe and proven but cheaper than 5-10k$ for just a serial connection.(CP341+Chipset)

The 1200 seem faster with more memory than a 200 because my application would need 2 S7-224 to fitted in and i want to have just 1 plc.
When i look to the processing time

200 = 0.22us for bit operation
1200 0.1us for bit 12us for word and 18us for float
312 0.1 us for bit 0.12us for word 0.16us for float

I wonder if it is a print error or the 1200 is really 100times slower than a 312 ?

Mike_RH · Jan 17, 2012

Jeff,

If you were thinking of using a couple of S7-200, the 1200 will work fine and be cheaper. You could then use the 1200 as a PN IO device for the 315 PN/DP you mentioned.

There are also ET200S serial module that may do what you want 6ES7 138-4DF11-0AB0 http://support.automation.siemens.com/WW/view/en/20270713

As far as execution times 312 vs S7-1200 I found these numbers on the support site:

S7 312 CPU processing times
for bit operations, min. 0.1 µs
for word operations, min. 0.24 µs
for fixed point arithmetic, min. 0.32 µs
for floating point arithmetic, min. 1.1 µs

S7 1200 CPU processing times
for bit operations, min. 0.1 µs; / Operation
for word operations, min. 12 µs; / Operation
for floating point arithmetic, min. 18 µs; / Operation

JesperMP · Jan 18, 2012

How about an IM151-8 CPU + the ET200S 1SI module ?

Same programming as S7-300 that you already know.
Much cheaper than S7-300.
Has ethernet in stead of lame MPI.
Expands via Profinet.
Almost same performance as 315-2PN/DP. Much faster then S7-200 or S7-1200.

Is a no-brainer IMHO.

Jeff23spl · Jan 18, 2012

JesperMP said:
How about an IM151-8 CPU + the ET200S 1SI module ?

Same programming as S7-300 that you already know.
Much cheaper than S7-300.
Has ethernet in stead of lame MPI.
Expands via Profinet.
Almost same performance as 315-2PN/DP. Much faster then S7-200 or S7-1200.

Is a no-brainer IMHO.

i didn't know that Et200 has a modbus module availaible...
I'll look for that 1SI...
I even worked with et200s cpu with good result, i'm just afraid of the module looking a little bit weak...

The cheapest way to achieve Modbus RTU with an S7-300 processor ?

Jeff23spl

Member

Mike_RH

Lifetime Supporting Member

KalleOlsen

Member

KalleOlsen

Member

Pudden

Member

Bratt

Lifetime Supporting Member

Jeff23spl

Member

Mike_RH

Lifetime Supporting Member

Lare

Member

Homer_BL

Member

Pudden

Member

Jeff23spl

Member

Mike_RH

Lifetime Supporting Member

JesperMP

Lifetime Supporting Member + Moderator

Jeff23spl

Member

Similar Topics