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ASCII and Modbus


iman hermansyah
 

Hi Gusys,

Iam a new comer in electronic world...
Could somebody teach me what is differencies between
ASCII text and Modbus,for inter-device communication.
Is there an interface for these?

Thank's

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Jim Purcell
 

iman,

Could somebody teach me what is differencies between
ASCII text and Modbus,for inter-device communication.
Now quite frankly I haven't heard of Modbus. I can tell you
that ASCII, American Standard Code for Information Interchange,
is simply a numeric code for letters, numbers, a few special
characters and some control characters. ASCII is widely used,
probably the standard, in the US. I would think that it may be
the standard for the world now, to have to convert among
various codes in international message handling would seem
an herculean task. When comparing communication codes
there are a number of considerations. Back when this sort
of communication was far less reliable the EBCDIC code
was sometimes used because it was more easily error
checked. I have never worked in an environment where
EBCDIC was in use.

Other considerations might be, what kind of information
is being transmitted. I don't know what is done to ASCII
when special characters are required, ones that look
strange to us who are accustomed only to English.

I haven't answered your question, but at least you know that
your message was received. This forum seems to have people
of widely varied skills and knowledge, I'm certain that someone
will be able to help you. It might help if you told us the context
in which you know about the Modbus code.

Is there an interface for these?
If the only difference between two code is the numerical values
conversion is quite simple. A look up table is often used, the
position in the table for one code is matched with the position
in the other table. A program has two pointers, one pointed
at the start of each table. The first table is searched
while incrementing both pointers until a match is found.
Then the value pointed to by the second pointer is the
converted character. There may be some programmers
in the group who know a more sophisticated conversion
scheme. I've never needed one.

Jim


iman hermansyah
 

Thank's Jim,

I just red the instruction,Modbus is a protocol for
data tranfering. It's a standard protocol comunication
which created by Modicon.Presently i've problem to
establish communication between 2 communication which
different protocol,one is ASCII and the other is
modbus.FYI i use RS-485 for this comm.
Anyway i'm getting clear in ASCII code.

Iman.
--- Jim Purcell <jpurcell@...> wrote:
iman,

Could somebody teach me what is differencies
between
ASCII text and Modbus,for inter-device
communication.

Now quite frankly I haven't heard of Modbus. I can
tell you
that ASCII, American Standard Code for Information
Interchange,
is simply a numeric code for letters, numbers, a few
special
characters and some control characters. ASCII is
widely used,
probably the standard, in the US. I would think that
it may be
the standard for the world now, to have to convert
among
various codes in international message handling
would seem
an herculean task. When comparing communication
codes
there are a number of considerations. Back when this
sort
of communication was far less reliable the EBCDIC
code
was sometimes used because it was more easily error
checked. I have never worked in an environment where
EBCDIC was in use.

Other considerations might be, what kind of
information
is being transmitted. I don't know what is done to
ASCII
when special characters are required, ones that look
strange to us who are accustomed only to English.

I haven't answered your question, but at least you
know that
your message was received. This forum seems to have
people
of widely varied skills and knowledge, I'm certain
that someone
will be able to help you. It might help if you told
us the context
in which you know about the Modbus code.

Is there an interface for these?
If the only difference between two code is the
numerical values
conversion is quite simple. A look up table is often
used, the
position in the table for one code is matched with
the position
in the other table. A program has two pointers, one
pointed
at the start of each table. The first table is
searched
while incrementing both pointers until a match is
found.
Then the value pointed to by the second pointer is
the
converted character. There may be some programmers
in the group who know a more sophisticated
conversion
scheme. I've never needed one.

Jim



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Jim Purcell
 

iman,

I just red the instruction,Modbus is a protocol for
data tranfering.
So is ASCII, can you say something about where or why
it is used instead of ASCII?

which created by Modicon. Presently i've problem to
establish communication between 2 communication which
different protocol,one is ASCII and the other is
modbus.FYI i use RS-485 for this comm.
Anyway i'm getting clear in ASCII code.
The first thing you could do is locate a table for both and compare the
two. If you had two tables in memory, one ASCII, the other Modbus.
Another table would contain the jump addresses to the code to which
you are converting. Say you're converting ASCII to ModBus. The first
character comes along, and pointers point to ASCII and the jump table.
The convert program compares each the incoming ASCII character
with one in the ASCII table. If no match is found both pointers are
incremented. This repeats until a match is found, at which time the
second pointer should be pointing to the correct jump table value
enabling the program to load the alternate code into the accumulator
(or a variable in high level language. ) and send it wherever it is
supposed to go. Then pointers are resent and the next character
retrieved, etc.

Jim


 

--- In Electronics_101@y..., iman hermansyah <iman_hermansyah@y...>
wrote:
Hi Gusys,
Hi Imam,
My name is Anand Ahuja. As you have come to know by now, ASCII is
representation of various characters, including space, special and
control characters, in memory of computers.
Modbus is a communication protocol which works on RS485 bus. RS485
bus has different other protocols also which are used for
communication. RS485 bus is a two wire bus which is used in
industrial control for communication between various devices like a
PLC, temp. controller, electrical power monitor, AC or DC Drive, HMI
(Human Machine Interface).
The Modbus protocol uses ASCII characters for transfer of data between
devices. Besides, a protocol has other parameters like no. of bits,
parity, stop bits, baud rate, error checking and correction. Profibus
(from Siemens), Devicenet and Controlnet (from Allen Bradley) are
among the other protocols that are implemented on the same RS485 bus.
However, all of them cannot be implemented on the same bus. All the
devices sitting on the RS485 bus can be configured to communicate on
the same protocol. Each protocol has certain variations like no. of
bytes sent per packet, error checking, transmission speed,
master/slave or peer-to-peer mode, etc.,.

I hope that I have clarified your point.

Anand Ahuja

Iam a nandew comer in electronic world...
Could somebody teach me what is differencies between
ASCII text and Modbus,for inter-device communication.
Is there an interface for these?

Thank's

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Make a great connection at Yahoo! Personals.


Jim Purcell
 

anand,

I hope that I have clarified your point.
So it sounds like there is no conversion between ASCII
and Modbus, it's apples and oranges time.

Jim


iman hermansyah
 

Jim & Anand,

I'm getting more clearly about this,
Anand u're right this modbus i'll use for
communication a DCS ( Distributed Control System) and
a controller.This DCS is one of ABB product and the
controller is a product of Altronic.Unfortunetly the
controller use ASCII protocol to comunicate.
Another question,How many bits a register in ASCII,is
ASCII have stop bit,parity bit as MODBUS has ?

I'm so sorry if my question looks so sily,frankly i'm
really a beginner in this matter.

Thank's,
iman
--- Jim Purcell <jpurcell@...> wrote:
anand,

I hope that I have clarified your point.
So it sounds like there is no conversion between
ASCII
and Modbus, it's apples and oranges time.

Jim


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Make a great connection at Yahoo! Personals.


Jim Purcell
 

iman,

Unfortunetly the
controller use ASCII protocol to comunicate.
Another question, How many bits a register in ASCII,is
ASCII have stop bit,parity bit as MODBUS has ?
First off, stop bits have to do with seriel communication
and as far as I know have nothing to do with the code.
ASCII is a seven bit code in some systems, the extra
bit is used for error detection, in others that bit
allows for ANSI characters. Look at a good computer
book and it will show those characters, in decimal they
begin at 128.

Jim