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Modbus is probably the most spread
serial protocol in industry Modbus solutions
from ME Advise
MCS is the exclusive reseller of MODBUS slave solutions from ME
Advise.
Modbus is probably the most spread
serial protocol in industry. Most devices, being able to communicate serial,
talk Modbus.
The communication is master / slave
driven. Modbus is capable to run full-duplex RS232 lines and half-duplex RS485
solutions. Also newer implementation variants run via Ethernet & TCP/IP.
One of the best sources for more
detailed information’s is http://www.Modbus.org/
A typical Modbus telegram shown in hex
characters is:
Request from master 02 03 00
08 00 01 05
FB
with the answer from slave 02 03
02 02 01 3C
E4
It’s to slave 02 request 03,
to send back from his address 0008,
one word (00
01), with checksum 05
FB, and from slave 02
answer 03,
with 02 bytes,
the values 02 01,
and checksum 3C
E4.
If you want to give your application an
easy connectivity to most of the worlds devices, so you should choose Modbus at
your first thought.
The application is purely BASCOM Basic.
It’s a software implementation for Atmel AVR controllers. The smallest, fully
tested version is for AVR 2313 with RS485, running the board you see below.
All here presented modules are the slave
implementation, but you can easily change to your specific master
implementation.
All written in pure BASCOM Basic.
Well / fully documented code.
' This is a empty shell to make the
download possible.
' You must not compile this under no circumstances.
' It is only used for as loading shel and to discribe
you how to use it.
See Test Procedure Bellow !!!!!!!!
' -----[ Program Description
]--------------------------------------------------
'
' This program implements the ModBus RTU protocol in an
universal I/O device
' It uses a special designed HW or STK200 development
kit for testing purpouse.
' It's a polled slave with 16 in and 16 outputs.
'
' -----[ Disclaimer
]-----------------------------------------------------------
'
' This example is offered on an "AS IS"
basis, no warranty expressed or implied.
' The programers disclaim liability of any damages
associated with the use of
' the hardware or software described herein.
' You use it on your own risk. We are not able to
provide any free support.
'
' Copyright (c) 2003 Mike Eitel all rights reserved
'
' -----[ Revision History
]-----------------------------------------------------
'
' 030410 - Version AVRMODDIO16 Ver 1.50 slave mclib 2313 ERAM Mike
Eitel
' *****[ conditional compiler flags
]*******************************************
Const
Stk200 = 1 ' When 1 then STK200 else DTR103
' *****[ conditional TEST flag
]************************************************
$regfile = "2313def.dat"
' Define serial communication parameters
$baud = 9600 ' ModBus speed
$crystal = 4000000 ' Frequency of unit
' -----[ Aliases
]--------------------------------------------------------------
' -----[ Constants
]------------------------------------------------------------
' Telegramms solved
' This device is capable of max 4 bytes data transfer mode 03 & 16 !!!
'
' Request Read Holding Register(03) SS 03
SH SL PH PL CL CH
' Answer Read
16 Holding Register(03) SS 03 BC 1H
1L CL CH
' Answer Read
32 Holding Register(03) SS 03 BC 1H
1L 2H 2L CL CH
' ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
' DB( 1 2 3 4 5 6 7 8 9 )
'
' Request Preset Single Register(06) SS 06 RH RL 1H 1L CL CH
' Answer Preset
Single Register(06) SS
06 RH RL 1H 1L CL CH
' ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
' DB( 1 2 3 4 5 6 7 8 )
'
' Request Preset Multiple Register(16) SS 10 SH SL PH PL BC 1H 1L 2H 2L CL CH
' Answer Preset
Multiple Register(16) SS 10 SH SL
PH PL CL CH
' ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
' DB( 1 2 3 4 5 6 7 8 9 10 11 12 13 )
'
' ' SS = Slave Address
' ' 03 = Command 03
' ' SH = Starting Address High
' ' SL= Starting Address Low
' '
PH = Nr. of Points High
' ' PL = Points Nr.(16 bits) Low
' ' BC = Byte Count
' ' 1H = Data 1 High
' '
1L = Data 1 Low
' ' 2H = Data 2 High
' ' 2L = Data 2 Low
' ' CL = CRC Low
' ' CH = CRC High
' -----[ Initialization
]---------------------------------------------
'
' Define port parameters
' Port B Is Used as output to LED of STK200
' Port D is used for communication and for latch controll
' Ddrd.0 ' RXD
' Ddrd.1 ' TXD
' Ddrd.2 ,
3, 4, 5 are usable switches of the STK200
' Ddrd.6 ' Enable for RS422 send pin
' Ddrd.7 ' NC for 2313
Datas(adressparamter) = Myaddress '
Set new Slave address
Datas(parameters) = Myparameter '
Set new Slave parameters
#if Stk200 '
***** TEST MODE ***
Datas(adressparamter) = 2 ' Set test address
Datas(parameters) = 4 '
Set test parameters
#endif ' ***** TEST MODE ***
'------[ Program
]----------------------------------------------------
'
Routine for Inputs
Datas(1) = '
Read allowed swiches
'
Routine for counting input changes
Datas(7) = Datas(1) And Datas(parameters) ' Check only
'
Routine for Outputs
'
If datas(5) is requesting high input pin, force output high. When input
'
reaches high level forcing is surpressed.
'
Generally output is OR overwriten high by normal output setting datas(3)
Portb = Not [(datas(5) And Not
Datas(1) ) Or
Datas(3) ]
' And how to you make a test?
' 1. Place 2313 into STK200 and switch on
' 2. First you use the load to AVR without compiling
' 3. Choose your modbus master source and send to this
slave with address 02
' In this description I talk from bytes, cause
depending from used application
' U will use registers starting with register 0001.
Sometimes the start with
' 10000 or higher. Please find that yourself, by
monitoring the telegram.
' Inputs
' Test input switches by reading from bytes 00 00.
Pressing the middle 4 switches
' will show a changed telegram status.
' The so called parameter is preset to monitor the
activities of switch PD2.
' Each movement on that switch will increase value of
bytes 00 06
' When you read from byte 00 0E you will see an
incremented word counter.
' Outputs
' Test normal output functionality by sending to
address 00 02. You can control
' result by LED status.
' Test fast output position control reaction by using
bytes 00 04. As soon as
' you set a bit you will see LED going on, ( I propose
PB4 ) and if you press
' according input ( PD4 ) the LED will switch off.
' Changing parameters
' If you write to byte 00 09 you can change slave
address. And if you write to
' byte 00 08 you can change the surviewed switches.
These changements are per-
' manetely stored in EERAM but are overwriten when
device is powered up.
' This sample will stop working after ca. 3 minutes.
You have to do reset AVR !!
' Have fun M. Eitel
- Baudrate 9600 8,N,1. Change baudrate
in code prepared
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- RS485 control included, RS232 also
working.
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- Telegrams solved: 3, 6 16 = 16
bit word and 32 bit long register access possible.
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- Slave address remote programmable,
stored in EERAM.
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- Always accepted default slave
address: FE to set address and
parameters.
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- Fully independent interrupt driven, send and receive communication.
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- Independent command detection
buffer.
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- 16 Byte Data Array from starting
from R0001 implemented.
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- Time based I/O multiplexing included
for 16 in and 16 outputs.
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Programmable signal counter for first 8
input pins.
Running layout as base of your
development available.
Me, Mike Eitel, I’m in industrial
business since 1981 and have done a lot of jobs. When I came in contact with
Atmel’s AVR, I landed soon at BASCOM. And I’m using that compiler since
August 1999 and [ as I’m too old
to be a genius ;-) ] I’m used to write a lot of comments.
Beside of the AVR, I’m a specialist
for industrial solutions, especially when they need a control system with high
level HMI, or most commonly called SCADA system. Made some nice implementations.
For some years I sold a SW called Wizcon, distributed by Axeda www.axeda.com.
Still using Wizcon, nothing was more logical, than making a connection between
my AVR projects and that PC based visualization. For reasons I explained before,
I choose Modbus as best protocol, realize and test my applications that way. I
meantime I have a AVR family solution with 8515 with LCD and 8535 with PID
regulators. The bigger processors run additionally multitasking. Works fine!
Support email: michael.eitel@schweiz.ch
Modbus generals.
1
Modbus
slave for AVR 2312.
1
ME
Advise.
3
Content
4
Module
/ label explanation:
5
Conditional
compiler flags.
5
Define
serial communication parameters.
5
Telegramms
solved.
5
Other
parameters.
6
Pseudo
constants programmed via telegram..
6
Important
Variables.
6
Define
port parameters.
6
Setup
interrupts.
7
Transfer
from ERAM slave address and parameters.
7
_com_z:
7
_com_1:
7
_com_2:
8
_com_4:
8
Subroutine
for sending values.
9
_send:
9
_again:
9
Interrupt
routine for preparing serial port
9
Interrupt
routine for reading serial input
10
Interrupt
routine for sendig serial output
10
Interrupt
routine for multiplexing In / Outputs.
10
$regfile = "2313def.dat"
This is compiled for AVR 2313
$lib "Modbus.lbx"
The checksum is calculated via marks
routine
Const Test = 1 '
When 1 then Test modus
Allows working without existing I/O
chips
Const Stk200 = 1 ' When 1 then STK200 else DTR103
This allows working with STK200 and
RS232 without having the board.
$baud = 9600 ' Modbus speed
#if Stk200
$crystal = 4000000
Ubrr = 25 ' For 9600 baud
#else
$crystal = 8000000
Ubrr = 51 ' For 9600 baud
#endif
This device is capable of max 4 bytes
data transfer in mode 03 or mode 16. Otherwise the receive and send buffers are
to small
Two sorts of communication are solved:
Reading
data in 16 bit and 32bit request via the telegram 03
and
Sending
16 bit data via telegram 06 and 32bit
via telegram 16.
Request Read Holding Register(03) SS
03 SH SL PH PL CL CH
Answer Read 16 Holding Register(03)
SS 03 BC 1H 1L CL CH
Answer Read 32 Holding Register(03)
SS 03 BC 1H 1L 2H 2L CL CH
¦
¦ ¦ ¦ ¦
¦ ¦
¦ ¦
DB(
1 2 3 4
5 6
7 8
9 )
Request Preset Single Register(06) SS 06 RH RL 1H 1L CL CH
Answer Preset Single Register(06) SS 06 RH RL 1H 1L CL CH
¦
¦ ¦ ¦ ¦
¦ ¦
¦
DB(
1 2 3 4
5 6
7 8
)
Request Preset Multiple Register(16) SS 10 SH SL PH PL BC 1H 1L 2H 2L CL CH
Answer Preset Multiple Register(16) SS
10 SH SL PH PL CL CH
¦
¦ ¦ ¦ ¦
¦ ¦
¦ ¦ ¦ ¦
¦ ¦
DB(
1 2 3
4 5
6 7
8 9
10 11 12 13
SS = Slave Address
03 = Command 03 as example for a telegram
type 03
BC = Byte Count. In some telegrams existing
byte counter
SH = Starting Address High of the AVR data
area
SL= Starting Address Low
PH = Number of Points High or general spoken
number of requested word data’s
PL = Points Nr.(16 bits) Low
CL = CRC Low. Checksum according Modbus low
nibble
CH = CRC High
1H = Data 1 High
1L = Data 1 Low
2H = Data 2 High
2L = Data 2 Low
Const Initializing = &HFE
The device will always react on this
address. It is foreseen to make initial programming of device parameters and
address: Myaddress.
Const Adressparamter = 10 '
Slaveparameters position
Const Parameters = 9 ' Slaveparameters position
These pointers define the position in
the data’s volatile RAM array
Const Dataarea = 16 '
Databuffer + 2 Slaveparameters
This is the size of the data area.
Const Savetoeram = 10 '
Address of Myaddress
This pointers are used to define the
position in EERAM.
Const Maxchar = 19 '
Nr. of characters for serial buffer
Size of the receive ring buffer
Const Telegrambytes = 14 '
Nr. of transmitted Bytes
Max length of the used telegrams. More
important in the bigger devices like 8515.
Const Pause = 2 '
Wait time before answer
A small device like this AVR reacts to
fast for a SCADA system. With this parameter you adjust a small wait time for
the answer telegram.
Dim Myaddress As Eram Byte At &H02 '
Address for this node (2-253)
Dim Myparameter As Eram Byte At &H03 ' Address for this node (2-253)
Dim Bytebuffer(maxchar) As Byte '
Receive serial-buffer
Dim Db(telegrambytes) As Byte '
Data’s in telegram
Dim Sdb(telegrambytes) As Byte '
Data’s in send telegram
Dim Datas(dataarea) As Byte At &H60 '
Place to keep the dynamic data’s
Port B Is Used For Data Exchange With
The Latches
'Ddrb = &HFF ' WRITE to multiple I/O Data port
'Ddrb = &H00 ' READ from multiple I/O Data port
Port D is used for communication and for latch controll
Ddrd = &B01111100 ' Set Portd Pin 2..6 as Outputs
‘ Ddrd.0 ' RXD
' Ddrd.1 ' TXD
' Ddrd.2 ' Strobe Enable Read chip 1
' Ddrd.3 ' Strobe Enable Read chip 2
' Ddrd.4 ' Strobe output latches Allegro UCN 5801A 1
' Ddrd.5 '
Strobe output latches Allegro UCN 5801A 1
' Ddrd.6 ' Enable for RS422 send pin
' Ddrd.7 ' NC for 2313
Allow receive & transmit ISR
Config Timer0
Datas(adressparamter)
= Myaddress ' Set new
Slave address
Datas(parameters)
= Myparameter '
Set new Slave parameters
Startingpoint for telegrams
If received address is this node or the
general initialization address, read next Byte from master, if not return to
start
If next character is one of the three
solved commands wait for next chars or restart
Select Case Db(2)
Case 3 : ' A read command
Case 6 : ' A write command
Case 16 : ' A write command
Else com_z '
Wrong command = restart
Else ' Wait for next incoming data
Get telegram into binary mode
Clear the receive buffer to make a
calculated response possible
Check the CRC of the message for errors
No CRC errors in packet so check what to
do and start reading / writing
Select Case of telegram
Case 03 : ' READING datas 1..n
' Request Read Holding
Register(03) SS 03 SH SL PH
PL CL CH
' Answer Read 16 Holding
Register(03) SS 03 BC 1H 1L
CL CH
' Answer Read 32 Holding
Register(03) SS 03 BC 1H 1L
2H 2L x x CL CH
Gosub _send ' Give answer
Goto _com_z ' All done, go back to Start
Case 06 : ' WRITING data’s 16 bit
' Request Preset Single Register(06) SS 06 RH RL 1H 1L CL CH
' Answer Preset Single Register(06) SS 06 RH RL 1H 1L CL CH
Gosub _send ' Give answer
Goto _com_z ' All done, go back to Start
Case 16 : '
WRITING data’s 1..n
'
Request Preset Multiple Register(16) SS 10 SH SL PH PL BC 1H 1L 2H 2L CL CH
' Answer Preset Multiple Register(16) SS 10 SH SL PH PL CL CH
Gosub _send ' Give answer
Goto _com_z ' All done, go back to Start
End
Select
Goto _com_z ' Not identified command
Start CRC generate routine and calculate
CRC for all sending bytes
Send Packet To Master , Including The
Sync Byte
On powerup it's treated once !
Read into serial ring buffer
Send contents from buffer
Timer0_isr: ' Controlls the multiplexing of data versus I/O's
' Port D is used for communication and for latch controll
' Ddrd.2 ' Strobe Enable Read chip 1
' Ddrd.3 ' Strobe Enable Read chip 2
' Ddrd.4 ' Strobe output latches Allegro UCN 5801A 1
' Ddrd.5 ' Strobe output latches Allegro UCN 5801A 2
' Ddrd.6 ' Enable for RS422 send pin
Select Case
Case 0: ' READ 1 --- High Byte ---
Case 1: ' READ 2 --- Low Byte ---
Case 2: ' WRITE 3 --- High Byte ---
Case 3: ' WRITE 4 --- Low Byte ---
Additional features:
1. When slave address is FF means not yet programmed, a HW test is possible,
by cause signal of input 1..16 is
copied to output 1..16.
2. The one byte parameter defines by AND function with input 1..8 counts up
a counter (bytes 07 and 08 ) at each signal change.
Order code : MODBUS-2313 |
