Lumel RE15 User manual

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USER’S MANUAL
SERIAL INTERFACE
WITH MODBUS PROTOCOL
MICROPROCESSOR
CONTROLLER
RE15

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CONTENTS
1. PREFACE ............................................................................... 4
2. DESCRIPTION OF THE MODBUS PROTOCOL .................... 4
2.1. ASCII framing ................................................................. 6
2.2. RTU framing ................................................................... 6
2.3. Characteristic of frame fields ....................................... 7
2.4. LRC checking ................................................................ 9
2.5. CRC checking ................................................................ 9
2.6. Character format in series transmission .................... 10
2.7. Transaction interruption .............................................. 10
3. DESCRIPTION OF FUNCTIONS .......................................... 11
3.1. Readout of N-registers (Code 03) .............................. 11
3.2. Writing of values into the register (Code 06) ............. 12
3.3. Writing into N-registers (Code 16) .............................. 13
3.4. Report identifying the device (Code 17) ..................... 13
4. ERROR CODES .................................................................... 15
5.TABLE OF REGISTERS FOR THE RE15 CONTROLLER ..... 17
AFFIX A. CALCULATION OF THE CHECKSUM .................... 23

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1. PREFACE
The RE15 microprocessor controller destined to measure and
control physical quantities is provided with a serial interface in
RS-485 standard for the communication with other devices.
The asynchronous communication MODBUS protocol has been
implemented on this serial interface.
The configuration of serial interface parameters has been
described in the Users Manual of the R15 controller.
Composition of serial interface parameters concerning RE15
controller:
•Controller address - 1 ... 247
•Baud rate - 2400, 4800, 9600 bits/s,
•Working modes - ASCII, RTU,
•Information unit - ASCII: 8N1, 7E1, 7O1;
and RTU: 8N2, 8E1, 8O1,8N1
•Maximal turnaround time - 1s
Explanation of some abreviations:
ASCII = American Standard Code
for Information Interchange
RTU = Remote terminal Unit
LRC = Longitudinal Redundancy Check
CRC = Cyclic Redundancy Check
CR = Carriage Return
LF = Line Feed (Character)
MSB = Most Significant Bit
Checksum = Control Sum
2. DESCRIPTION OF THE MODBUS PROTOCOL
The MODBUS interface is a standard adopted by manufacturers of
industrial controllers for an asynchronous character exchange of
information between different devices of measuring and control
systems. It has such features as:

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vSimple access rule to the link based on the master-slave
principle,
vProtection of transmitted messages against errors,
vConfirmation of remote instruction realisation and error
signalling,
vEffective actions protecting against the system suspension,
vTaking advantage of the asynchronous character transmission.
Programmable controllers working in the MODBUS system can
communicate with each other, taking advantage of the
master-slave protocol type, in which only one device (the
master - superior unit) can originate transactions (called
queries), and others (slaves  subordinate units) respond only to
the remote query by supplying the requested data to the
master. The transaction is composed of the transmitted command
from the master unit to the slave unit and of the response
transmitted in the opposite direction. The response includes data
demanded by the master or the realised confirmation of its
command. Master can transmit information to individual slaves, or
broadcast messages destined for all subordinate devices in the
system (responses are not returned to broadcast queries from the
master).
The format of transmitted information is as follows:
 master => slave: device address, code representing the
required command, data to be sent, control
word protecting the transmitted message,
 slave => master: sender address, confirmation of the command
realization, data required by the master,
control word protecting the response
against errors.
If the slave device detects an error when receiving a message, or
cannot realize the command, it prepares a special message about
the error occurrence and transmits it as a response to the
master.
Devices working in the MODBUS protocol can be set into the
communication using one of two transmission modes: ASCII or RTU.
The user chooses the required mode, along with the serial port

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parameters (baud rate, information unit) during the configuration of
any device.
In the MODBUS system, transmitted messages are placed into
frames that are no related to serial transmission. These frames have
a defined beginning and end. This enables for the receiving device
to reject incomplete frames and the signalling of related errors with
them.
Taking into consideration the possibility to operate in one of these
two different transmission modes (ASCII or RTU), two frames have
been defined.
2.1. ASCII framing
In the ASCII mode each byte of information is transmitted as two
ASCII characters.
The basic feature of this mode is that it allows to long intervals
between characters within the message (to1sec) without
causing errors.
A typical message frame is shown below:
Start Address Function Data LRC End
beginning check index
index
1 char : 2 chars 2 chars n chars 2 chars 2 chars CR LF
In ASCII mode, messages start with a colon character (: -ASCII
3Ah) and end with a carriage return-line feed (CR and LF
characters). The frame information part is protected by the LRC code
(Longitudinal Redundancy Check).
2.2. RTU Framing
In RTU mode, messages start and end with an interval lasting mini-
mum 3.5 x (lasting time of a single character), in which
a silence reigns on the link.
The simplest implementation of the mentioned time interval
character is a multiple measure of the character duration time at the

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set baud rate accepted on the link.
The frame format is shown below:
Start Address Function Data CRC End
bedinning check index
index
T1-T2-T3-T4 8 bits 8 bits n x 8 bits 16 bits T1-T2-T3-T4
Start and end indexes are marked symbolically as an interval equal
to four lengths of the index (information unit). The checking code
consists of 16 bits and emerges as the result of CRC calculation
(Cyclical Redundancy Check) on the frame contents.
2.3. Characteristic of frame fields
Address field
The address field of a message frame contains two characters
(in ASCII mode) or eight bits (in RTU mode).
Valid slave device addresses are in the range of 0-247 decimal. The
master addresses the slave units by placing the slave
address in the frame address field. When the slave sends its
response, it places its own address in the frame address field what
enables the master to check which slave is responding. The 0
address is used as a broadcast address recognized by all slave
units connected to the bus.
Function field
The function code field of a message frame contains two
characters (in ASCII mode) or eight bits (in RTU mode). Valid codes
are in the range of 1-255 decimal. When a message is sent from a
master to a slave device, the function code field tells the slave what
kind of action to perform. When the slave responds to the master, it
uses the function code field to indicate and confirm either a normal
(error-free) response or that some kind of error occurred and the
realization of the command is impossible.
For a formal response the slave simply echoes the original function
code. In case of an error assertion, the slave returns a special code
that is equivalent to the original function code with its most

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significant logic 1. The error code is placed on the data field of the
response frame.
Data field
The data field is constructed using sets of two hexadecimal digits, in
the range of 00 - FF hexadecimal.
These can be made from a pair of ASCII characters or from one
RTU character, according to the networks serial transmission mode.
The function code range is 1-255. The data field of messages sent
from a master to slave devices contains additional information which
the slave must use to take the action defined by the function code.
This can include items like discrete and register addresses, the
quantity of items to be handled, and count of actual data bytes in the
field, a.s.o. The data field can be non-existent (of zero length) in
certain kinds of frames. That occurs always when the operation
defined by the code does not require parameters.
Error checking field
Two kinds of error-checking methods are used for standard
MODBUS networks. The error checking field contents depends upon
the applied transmission mode.
When ASCII mode is used for character framing, the error
checking field contains two ASCII characters. The error check
characters are the result of a Longitudinal Redundancy Check (LRC)
calculation that is performed on the message contents
(exclusive of the beginning colon and terminating CRLF
characters). LRC characters are appended to the message as the
last frame field preceding the end markers (CR, LF).
When RTU mode is used for character framing, the error checking
field contains a 16-bit value implemented as two 8-bit bytes. The
error check value is the result of a Cyclical Redundancy Check
Calculation (CRC) performed on a message contents. The CRC field
is appended to the message as the last field in the message. When
this is done, the low-order byte of the field is appended first,
followed by the high-order byte. The CRC high-order byte is the last
byte to be sent in the message.

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2.4. LRC checking
The LRC is calculated by adding together successive 8-bit bytes of
the message, discarding any carries, and then two is complemen-
ting the result. It is performed on the ASCII message field contents
excluding the ,,colon character that begins the message, and
excluding the CR, LF pair at the end of the message. The 8-bit value
of the LRC sum is placed at the frame end as two ASCII characters,
first the character containing the higher tetrad, and after it, the
character containing the lower LRC tetrad.
2.5. CRC checking
The generating procedure of CRC is realised according the
following algorythm:
1. Load a 16-bit register with FFFFh. Call this the CRC register.
2. Take the byte from the data block and execute the EXOR
operation with the low-order byte of the CRC register. Place the
result into the CRC register.
3. Shift the CRC register contents one bit to the right (towards the
LSB), write 0 on the most significant bit (MSB=0).
4. Check the state of the lowest order bite (LSB) extracted from
the CRC register in the previous step. If its state is equal 0, then
follows a return to the step 3 (another shift).
If the LSB is equal 1, the operation EXOR of the CRC register is
executed with the polynomial value A001h.
5. Repeat steps 3 and 4 until 8 shifts have been performed. When
this is done, a complete 8-bit byte will have been processed.
6. Repeat steps 2 through 5 for the next 8-bit byte of the message.
Continue doing this until all bytes of the message have been
processed.
7. The final contents of the CRC register is the searched CRC
value.
8. When the CRC is placed into the message, its upper and lower
bytes must be swapped as described below.

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2.6. Character format during serial transmission
In the MODBUS protocol, characters are transmitted from the
lowest to the highest bit.
Organization of the information unit in the ASCII mode:
v1 start bit,
v7 data field bits,
v1 even parity check bit (odd) or lack of even parity check bit,
v1 stop bit at even parity check or 2 stop bits when lack of even
parity check.
Organization of the information unit in the RTU mode:
v1 start bit,
v8 data field bits,
v1 even parity check bit (odd) or lack of even parity check bit,
v1 stop bit at even parity check or 2 stop bits when lack of even
parity check.
2.7. Transaction interruption
In the master unit the user sets up the important parameter which is
the maximal response time on the query frame after which
exceeding, the transaction is interrupted. This time is chosen such
that each slave unit working in the system (even the slowest)
normally will have the time to answer to the frame query.
An exceeding of this time attests therefore about an error and such
treated by the master unit.
If the unit slave will find out a transmission error it does not
accomplish the order and does not send any answer. That causes
an exceeding of the waiting time after the query frame and the
transaction interruption.
In the R15 controller  maximal response time on the query frame is
equal 1 s.

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3. FUNCTION DESCRIPTION
In the R15 controller following protocol functions have been
implemented:
Code Signification
03 Reading of n-register
06 Writing of an individual register
16 Writing of n-registers
17 Slave device identification
3.1. Reading of n-registers (code 03)
Demand:
The function enables the reading of values included in registers in
being addressed slave device. Registers are 16 or 32-bit units,
which can include numerical values bounded with
changeable processes, and the like. The demand frame
defines the 16-bit start address and the number of registers to
read-out.
The maximal number of registers read out by one command is 128
for the RE15 controller.
The signification of the register contents with address data can be
different for different device types. The function is not accessible in
the broadcast mode.
The function is not accessible in the broadcasting mode.
Example: Reading of 3 registers beginning by the register with the
6Bh address.
Address Funtion Register Register Number of Number of Checksum
Address Hi Address Lo registers Hi registers Lo
11 03 00 6B 00 03 7E LRC

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Answer:
Register data are packing beginning from the smallest address: first
the higher byte, then the lower register byte.
Example: the answer frame
Adres Function Number Value Value Value Value Value Value Checksum
of bits in the in the in the in the in the in the
regist. regist. regist. regist. regist. regist.
107 107 108 108 109 109
Hi Lo Hi Lo Hi Lo
11 03 06 02 2B 00 00 00 64 55 LRC
3.2. Writing of values in the register (code 06)
Demand:
The function enables the modification of the register contents is
accessible in broadcast mode.
Example:
Address Function Register Register Value Value Checksum
address Hi address Lo Hi Lo
11 06 00 87 03 9E C1 LRC
Answer:
The correct answer to a value record demand in the register is the
retransmission of the message after accomplishing the operation.
Example:
Address Function Register Register Value Value Checksum
address Hi address Lo Hi Lo
11 06 00 87 03 9E C1 LRC

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3.3. Writing in n-registers (code 16)
Demand:
The function is accessible in broadcast mode. It enables the
modification of the register contents. The maximal number of
registers read out by one command is 128 for RE15 controller.
Example: Writing of two registers beginning from the register
addressed 136.
Address Function Regist. Regist. Number Number Number Data Data Data Data Checksum
address address of of of Hi Lo Hi Lo
Hi Lo regist. regist. bytes
Hi Lo
11 10 00 87 00 02 04 00 0A 01 02 45
Answer:
The correct answer includes the unit slave address, function code,
starting address and the number of recorded registers.
Example:
Address Function Register Register Number of Number of Checksum
address Hi address Lo registers Hi registers Lo
11 10 00 87 00 02 56 LRC
3.4. Report identifying the device (code 17)
Demand:
This function enables the user to obtain information about the device
type, status and configuration depending on this.
Example:
Address Function Checksum
11 11 DE LRC
Answer:
The field ,,Device identifier in the answer frame means the unique
identifier of this class of device, however the other fields include
LRC

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parameters depended on the device type.
The RE15 controller gives information related to additional inputs
and outputs.
Example concerning the RE15 controller
Slave Function Number Device Type of Type of Execution Checksum
address of bytes identifier additional output number2
input
11 11 4 68 xx1) yy2) 03)
1) XX - value as in the controller execution code - Item related
with the additional input
2) YY - four discontinuous output,
1 - one continuous output + three discontinuous outputs
2 - two continuous outputs + two discontinuous outputs
3) 0 - for standard execution, different from 0,
for custom-made executions.

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4. ERROR CODES
When the master device is broadcasting a demand to the slave
device then, except for messages in the broadcast mode, it expects
a correct answer. After sending the demand of the master unit, one
of the four possibilities can occur:
vIf the slave unit receives the demand without a transmission
error and can execute it correctly, then it returns a correct
answer,
vIf the slave unit does not receive the demand, no answer is
returned. Timeout conditions for the demand will be fulfilled in
the master device program.
vIf the slave unit receives the demand, but with transmission
errors (even parity error of checking sum LRC or CRC), no
answer is returned. Timeout condition for the demand will be
fulfilled in the master device program.
vIf the slave unit receives the demand without a transmission
error but cannot execute it correctly (e.g. if the demand is, the
reading-out of a non-existent bit output or register), then it
returns the answer including the error code, informing the
master device about the error reason.
vA message with an incorrect answer includes two fields
distinguishing it from the correct answer.
The function code field:
In the correct answer, the slave unit retransmits the function code
from the demand message in the field of the answer function code.
All function codes have the most-significant bit (MSB) equal zero
(code values are under 80h). In the incorrect answer, the slave unit
sets up the MSB bit of the function code at 1. This causes that the
function code value in the incorrect answer is exactly of 80h greater
than it would be in a correct answer.
On the base of the function code with a set up MSB bit the program
of the master device can recognize an incorrect answer and can
check the error code on the data field.

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The data field:
In a correct answer the slave device can return data to the data field
(certain information required by the master unit). In the
incorrect answer the slave unit returns the error code to the data
field. It defines conditions of the slave device which had produced
the error.
An example considering a demand of a master device: read out 4520
register (11A8h) and the answer of the slave unit: forbidden data
address, because the maximal register address in the RE15 con-
troller is 4519.
Data are in the hexadecimal shape.
Example: demand
Slave Function Variable Variable Number of Number of Checksum
address address address variables variables
Hi Lo Hi Lo
0A 03 12 BO 00 01 39 LRC
Example: answer
Address Function Error Checksum
0A 83 02 71 LRC
Possible error codes and their meanings are shown in the table
below.
Code Meaning
01 Forbidden function
02 Forbidden data address
03 Forbidden data value

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5. TABLE OF REGISTERS FOR THE RE15 CONTROLLER
In the RE15 controller data are placed in 16-bit registers.
Bits in the register are numbered from the lowest to the highest one
(b0-b15).
The list of registers are presented in the tabel 1.
Symbols R, W in the Option column signify allowable actions on the
controller data: R-readout, W-writing.
Table 1. Contents of 16-bit registers
Regist. Option Symbol Range Description
address
4000 R,W inpu 0...16 Output type: 0-PT100, 1-PT1000, 2-Ni100, 3-Cu100, 4-J,
5-T, 6-K, 7-S, 8-R, 9-B, 10-E, 11-N, 12-Chromel-copel,
13-resistance 0...400 W,14-0...20 mA, 15-4...20 mA,
16-0...10V, 17- 0...5V
4001 R,W t_lj 0, 1 0- 2-wire line, 1- 3-wire line
4002 R,W r_lj 0...200 Resistance of the line*10
4003 R,W Conp -1...501 Compensation of cold ends*10, ; values <0 or >500
mean automatic compensation
4004 R,W Lcpp 0, 1, 2 Number of digits after coma (value 2 for linear inputs)
4005 R,W Shjf -999...999 Shift of measured value1)
4006 R,W spll -999...splH Lower range of the measured value on the main input1)
4007 R,W splH Spll...9999 Upper range of the measured value on the main input1)
4008 R,W J2lo -999...J2Hj Lower range of the measured value on the additional
input1)
4009 R,W J2Hj J2lo...9999 Upper range of the measured value on the additional
input 1)
4009 R,W J2Hj J2lo...9999 Upper range of the measured value on the additional
input1)
4010 R,W Jnp 0...5 Range of the additional input: 0-0...20 mA; 1-4...20 mA;
2-0...10 V ; 3-0...5 V; 4-0...100 W; 5-0...1000 W;
4011 R,W Fjn 0...4 0 - set value (rsp = inp2); 1- extra information
measurement; 2- sum of signals from both inputs;
3 - difference with main input; 4- arythmetical mean
from both inputs
4012 R,W Fjnb 0...3 Function of the binary input: 0-no used binary input;
1- stops the control (control signal=0); 2- switch over
to the manual work, 3- program end; 4- program
stopped on the value counted lately

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4013 R,W Ouc 0...3 Range of the continuous output no I: 0-0-20 mA for
current outputs; 1-4-20 mA ; 2-0-10 V ; 3-0-5 V
4014 R,W Ouc 0...3 Range of the continuous output no II: as above
4015 R,W Out 0...18 Output function no 1: 0-no used, 1-Y1, 2-Y2-c, 3-Y2-S,
4-ahi, 5-alo, 6-dbhi, 7-dblo, 8-dbhl, 9-dbin,
10-Ahi2, 11-Alo2, 12-Eout, 13-EoP, 14-Err1,
15-Err2, 16-tri1, 17-tri2, 18-trsp
4016 R,W Out 0...18 Output function no 2: as above
4017 R,W Out 0...18 Output function no 3: as above
4018 R,W Out 0...18 Output function no 4: as above
4019 R,W Bar 0...4 Bargraph function no 1: 0- control signal Y1 0...100%;
1-control signal Y2 0...100%; 2-signal from the main input
spll...splh; 3-signal from the additional input
i2Lo...i2Hi; 4-set value spll...splh
4020 R,W Bar 0...4 Bargraph function no 2: as above
4021 R,W rsp 0, 1, 2 Kind of set value, 0- constant value, 1- programmed,
2- from the additional input
4022 R,W sp Depends Set value for the constant control1)
on the input
4023 R,W naro 0...999 Change speed of the set value during the soft-start*10
4024 R,W Nrpr 1...15 Program number executed for the programmed control
4025 W 0, 1, 2 Control of the program work:0-stop, 1-continue,
R 0, 1 2-start from the beginning
4026 R,W Pb 0...9999 Proportional band for the main line*10
4027 R,W Tj 0...3600 Integration time-constant
4028 R,W Td 0...1000 Differentiation time-constant
4029 R,W To 1...250 Cycle time
4030 R,W H0...999 Hysteresis for on-off control1)
4031 R,W pb-c 0...9999 Proportional band for the auxiliary line*10
4032 R,W Tj-c 0...3600 Integration time-constant for the auxiliary line
4033 R,W Td-c 0...1000 Differentiation time-constant for the auxiliary line
4034 R,W to-c 1...250 Cycle time for the auxiliary line
4035 R,W Hj-c 0...999 Hysteresis for on-off control of the auxiliary control 1)
4036 R,W Hn 0...999 Dead band for three-state control1)
4037 R,W typr 0,1 Kind of control: 0: inverse, 1- direct
4038 R,W y-of 0...1000 Correction of the control signal *10 (for the integration
time-constant ti=0)

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4039 R,W 1asp for sp Set value for the alarm on the output 11)
4040 R,W 1aHj 0...999 Hysteresis for the alarm on output 11)
4041 R,W 1apa 0,1 Storage of alarm no 1: 0-off, 1-on
4042 R,W 2asp for sp Set value for the alarm on the output 21)
4043 R,W 2aHj 0...999 Hysteresis for the alarm on output 21)
4044 R,W 2apa 0,1 Storage of alarm no 2: 0-off, 1-on
4045 R,W 3asp for sp Set value for the alarm on the output 31)
4046 R,W 3aHj 0...999 Hysteresis for the alarm on output 31)
4047 R,W 3apa 0,1 Storage of alarm no 3: 0-off, 1-on
4048 R,W 4asp for sp Set value for the alarm on the output 41)
4049 R,W 4aHj 0...999 Hysteresis for the alarm on output 41)
4050 R,W 4apa 0,1 Storage of alarm no 4: 0-off, 1-on
4052 R,W cont 0,1 Index of the constant control continuation after the
supply switching on, 0-control off, 1- control on
4053 R,W Auto 0,1,2 Self-adaptation algorythm: 0-without self-adaptation,
1-identyfying method, 2-oscillation method
4054... R,W lcyc 1...99 Number of program cycles p
4773 Register number r for the program p is equal:
address r =(p-1)*48+4054
of each R,W bloh 0...999 Blocking value in the program p1)
Register number r for the program p is equal:
r =(p-1)*48+4055
R,W Cont 0,1 Continuation of the program p after the supply decay:
0-stop, 1-continue, the register number r for the
program p is equal: r =(p-1)*48+4056
R,W naxx, 0...999 Change rate of the set value on the segment xx *10
The register number r for program p of the segment x is
equal: r =(p-1)*48+(x-1)*3+4057
R,W SPxx Range de- Set value on the end of the segment1), when the change rate > 0
or pends on the or hold time , when the change rate=0;
tixx input 0...999 The register number r for program p of the segment x is
equal: r =(p-1)*48+(x-1)*3+4058
R,W eoxx 0,1 Output y in the segment xx (bit y-1): 1-output on,
0-output off.
blxx, 0,1 Index for the active deadlock in the segment xx (bit 4)
xxx1xxx-1, 1-on, 0-off
The number of the register r for the program p of the
segment x is equal: r = (p-1)*48+(x-1)*3+4059

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4774 R Device state:
bit 0: 1- measured value on the main input is below the
lower input range or input short-circuiting
bit 1: 1- measured value on the main input is over the
upper input range or input opening
bit 2: 1- measured value on the additional input is below
the lower input range
bit 3: 1- measured value on the additional input is over
the upper input range
bit 4: output state no 1: 0-off, 1-on
bit 5: output state no 2: 0-off, 1-on
bit 6: output state no 3: 0-off, 1-on
bit 7: output state no 4: 0-off, 1-on
bit 8: 1- manual control, 0- automatic control
bit 9: 1-change of the set value, i.e. Soft-start
bit 10: 1- programmed control, 0- constant control
bit 11: 1- program execution, 0- program stopped
bit 12: 1- program blocking because of a too
high deviation
bit 13: binary input state: 0- open, 1- short-circuited
bit 14 and 15: position of decimal point:
00- without decimal point,
01- decimal on the position 1
10- decimal on the position 2 (see ref. 1) )
4775 R Measured value on the input no 11)
4776 R Measured value on the input no 21)
4777 R Controlled value1)
4778 R Set value (actual value)1)
4779 R h0...1000 Control value of the line I *10
4780 R c0...1000 Control value of the line II *10
4781 R n0...15 Number of the segment currently executed
for the programmed control
4782 R tTime remaining to the segment end
4783 R LNumber of program cycles remaining to the end
1) the value is multiplied by the multiplier depending on the
parameter value lcpp (position of the decimal point), i.e.:
when lcpp=0, then the multiplier =1;
when lcpp=1, then the multiplier = 10;
when lcpp=2, then the multiplier = 100.