SEP

The higher-level processor takes on the role of the master device. The connected SEP is always the slave. This configuration is firmly fixed and cannot be altered. So, as the standard MODBUS commands, the master cyclically polls individual slaves and processes their responses.

For orientation purposes we show the structure of normal packets and the principle of CRC generation:

Query (from master):

   |Adresa/8 |Funkce/8 |Start/16 |Number/16 |CRC/16 |

Response (from slave):

   |Adresa/8 |Funkce/8 |Count/8 |Data/8x count |CRC/16 |

The CRC uses polynomial 0xA001. It can be generated from a table or by means of a cycle and bit rotation. Generation using a table is eight times faster than a calculation in a cycle because there is no need for rotation of each byte in bits.

0x01 – READ_OUTPUT_STATUS

This function serves for reading binary outputs. Address space for this function is as follows:

Start: 0x00 - 0x07, 0xF0
Number:0x01 - 0x08 , at address 0xF0 1 is obligatory

These numbers represent the start address and number of required elements. It should be emphasised that the address sum and number of elements cannot exceed the highest possible address. Upon exceeding a random value outside the permitted range an EXCEPTION_RESPONSE is returned. This rule applies to all functions without exception.

0x02 – READ_INPUT_STATUS

This function serves for reading binary inputs. Address space for this function is as follows:

Start: 0x00 - 0xFF
Number:0x01 - 0x08

0x03 – READ_HOLD_REGS

Memory registers are read with this function. Internal flash memory, in which constants for analog inputs/outputs are stored, is also mapped into these registers. Address space for this function is as follows:

Start: 0x00 - 0x07
Number:0x01 - 0x08

0x04 – READ_INPUT_REGS

Analog inputs and counters are read with this function. Values (except for counters), returned by this function, are converted to the set range, i.e. the analog input range (e.g. 4– 20 mA) is converted to the size of the physical variable. Limits for conversion are stored in flash memory and they can be modified using program conf.exe. Each input can be configured separately. Counters can be set and reset. Address space for this function is as follows:

Start: 0x00 - 0x08 – for analog inputs
0x09 - 0x0A – for analog outputs
0x10 - 0x20 – for counters

Counters are read as normal 16-bit registers although their actual capacity is 32-bit. This means that it is a good idea to read at least two registers at a time (from even addresses) so that the complete contents of a counter are obtained.

It should also be emphasised that these counters have an order of bytes which is more jumbled than usual. A normal 32-bit word is organised as follows:

08:28:22.401|                 |69112202 69112201|S00I   OUT   58| 89 0user 
FF7E 0391 00A4 032C 02D6 0317 033D 02E3 02EE 000E 0016 0000 0000 0124 0000
                                                            ---- ----

As MODBUS is bit-oriented and not word-oriented the order of bytes becomes jumbled in counters. This fact should be taken into consideration in the higher level system. The order of bytes in counters now looks as follows:

08:28:22.351 tx      8 | S00
0104 0010 0010 F003
08:28:22.396 rx;i   37 | S00
0104 2024 0100 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0004 0000 
       -- ---- --

0x05 – FORCE_SINGLE_OUT

This function serves for setting binary outputs. Address space for this function is as follows:

Start: 0x00 - 0x07

0x06 – FORCE_SINGLE_OUT

Memory registers can be modified with this function. Since internal flash memory is also mapped into these registers this memory needs to be unlocked by making an entry to a “special binary output“. The memory is automatically locked again after a successful entry or after 10 sec. This prevents unwanted overwriting of the constant in SEP during labouring or in the case of an unsuitably programmed master. In practice this means two acts:

f the flash memory is not unlocked beforehand SEP will still acknowledge that the entry is correct but will not actually do anything. The state of memory locking can also be read with a 0xF0 binary output status request. Log. 1 signifies it is unlocked. It is not necessary to maintain the immediate order of unlocking, entry, as it is possible to insert the order of other queries between these two actions. It is only necessary to take automatic time locking into account. When setting up counters it is necessary to be aware that they are 32-bit counters and that the whole counter needs to be written to – two consecutive entries or use function 0x10.

Address space for this function is as follows:

Start: 0x00 - 0xFF – for flash
0x100 - 0x101 – for analog outputs
0x110 - 0x130 – for counters

0x0F – FORCE_MULTIPLE_OUTS

This function can be used to advantage for setting up binary outputs. This function is able to set up all outputs according to the applied mask. Address space is as follows:

Start: 0x00 - 0x07, 0xF0
Number:0x01 - 0x08, – at address 0xF0 1 is obligatory

0x10 – RESET_MULTIPLE_REGS

This function serves for mass setting of memory registers. What applies to function 0x06 applies to this function. Address space is as follows:

Start: 0x00 - 0xFF – for flash
0x100 - 0x101 – for analog outputs
0x110 - 0x130 – for counters
Number:0x01 - 0x08

This function is not yet fully supported. We recommend using multiple polling of function 0x06 (FORCE_SINGLE_REG) instead.

0x1E – READ_ALL

This new function was added to the protocol for easier overall control of SEP. The query/response pair enables the reading and setting of all inputs- outputs in one communication cycle. The form of queries and responses is somewhat different from the standard so a more detailed description is given below:

|Adresa/8 |Funkce/8 |Bin.Out/8 |An.Out1/16 |An.Out2/16 |Rez./8 |CRC/16 |

The states of binary and analog outputs are contained in a query, as is obvious. Binary states form an ordinary bit mask which is copied to SEP outputs after being correctly received. Analog values are first converted according to limits from flash memory and then set to the actual outputs.

|Addr/8|Funkce/8|Count/8|Bin.Out/8|Bin.In/8|An.In/9x16|An.Out/2x16|CRC/16|

Inputs and outputs in the response are up-to-date from the instant of reading from SEP. The temperature of the AD converter chip is also contained in analog inputs (input 0x08). Since this has a negligible temperature rise this data can be taken as the ambient temperature. This data is not converted because the unit is not designed for measuring temperature – it is up to the higher-level system how this value is handled.

This function enables one SEP to communicate with several different opposite stations. Digital and analog inputs are divided into 8 groups:

Skupina:   obsahuje tyto kanály:
  No        Din  Dout  Ain  Aout
  0         0    0     0    0
  1         1    1     1    1
  2         2    2     2
  3         3    3     3
  4         4    4     4
  5         5    5     5
  6         6    6     6
  7         7    7     7

Each group has its own target address defined in the “(g)roup parameters” menu. These addresses can only differ in the last byte. Each group has its own opposite group assigned. Addresses and groups at both ends of the radio link must be defined reciprocally; see the configuration example.

The threshold “ani” for analog inputs and “cnt” for counters are individually defined for each group. Fields (t)hr and (c)thr in the SEP parameters menu are not used in Group mode.

These are given in the separate article Protocol SEP for MORSE – examples.

A short example is given here only – the SEP packet and the Debug message at the parameter “(D)ebug level:1“:

Monitoring: source 690F0002|5.
07:05:11.532  INPUTS CHANGED. SENT TO 690F0001
state: di 007F do 0002 anai0 0066 anai1 0057 anai2 0049 anai3 0057 anai4 
005C anai5 0057 anai6 0049 anai7 0057 ao0 0000 ao1 000C
07:05:11.532|                 |690F0001 690F0002|S01I   OUT   58| 89 0user 
027F 0066 0057 0049 0057 005C 0057 0049 0057 0045 0000 000C 0000 004C 0000 
0004 0000 0000 0000 0000 0000 0000 0000 0000 0000 0019 0000 0000 8D66

The Debug message contains the state for Digital input, Digital output, Analog input, Analog output.

The SEP packet content:

0066 0057 0049 0057 005C 0057 0049 0057 – analog input 0 to 7

0000 004C 0000 0004 0000 0000 0000 0000 0000 0000 0000 0000 0000 0019 0000