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Cactus protocol for MORSE

version 8.08


1. Introduction

The Cactus protocol transfers the data between Master PLC Cactus and the Slaves PLCs. Data is transferred to the radio channel without being modified and is checked using the checksum.

2. Data Format

The items are composed from the hexadecimal numbers coded in ASCII. E.g. the item 0x3744 represents the hex numbres 0x7D.

Data frame structure and the example:

| IDENT/16 | SERV/16 | DATA | CHS/16 | CR/8 |
    3744     3039      3030   3836     0D

the Slave identity


the cactus service number


data, the even number of data pairs




end of frame, always 0x0D

Pooling call:

| IDENT/16 | CR/8 |
    3744     0D


| ACK/8 | CR/8 |
     21   0D

ackknowledge, 0x21 represents the ! symbol


end of frame, always 0x0D

No Acknowledge:

| NACK/8 | CR/8 |
     3F    0D

nonackknowledge, 0x3F represents the ? symbol


end of frame, always 0x0D

The checksum counting

The checksum is counted from the items IDENT, SERV and DATA. The process for all type of SERV except 0x1C:

Each byte of the frame represents one hex character according to ASCII table. The resulting hex characters in pairs are summed and the last two characters in ASCII form creates the checksum. Example:

3744 3039 3030 3836 0D … the frame with the type SERV = 3039 = 0x09

0x7D + 0x09 + 0x00 = 0x86

0x86 in ASCII is 3836 and this is the CHS/16

The process for type SERV 0x1C:

The bytes are summed in this form which is in the frame. Last two characters of the result are expressed in ASCII:

3744 3143 4148 4F4A 3131 0D … the type SERV = 3143 = 0x1C

0x 37 + 44 + 31 + 43 + 41 + 48 + 4F + 4A = 0x 211 -> 0x11

0x11 in ASCII is 3131 which is the CHS/16

3. Implementation in MORSE

The network arrangement.

CACTUS     CU 73112200                   CU 7311227D     CACTUS 7D
                              :          CU 7311227E     CACTUS 7E
                              :......... RADIOMASTER --- SLAVE

The PLC Cactus Master is connected by vires to the MORSE CU Radioslave which has the MORSE address ending with 0x00.

The PLC Cactus Slave having the identity e.g. 0x7D is connected to the CU Radiomaster. It uses the MORSE address ending with the same characters 0x7D. The higher part of MORSE address is the same as at CU Radioslave.

The traffic possibility:

Pooling in the quiet state

Master PLC sends the pooling call to the PLC Slave and it answers:

0x37440D  -->  0x37440D
0x37440D  <--  0x37440D

Request from MASTER and response from SLAVE

SLAVE PLC sends data only after request:

MASTER PLC                SLAVE PLC
0x37440D             -->  0x37440D
0x37443039303038360D <--  0x37443039303038360D
0x210D               -->  0x210D

RADIOSLAVE CU remembers the SLAVE identity after receiving the dataframe from SLAVE PLC to be able send the ACK from MASTER PLC to the appropriate SLAVE PLC. Only one ACK can be sent.

Data from MASTER

MASTER PLC can transmit spontaneously:

MASTER PLC                SLAVE PLC
0x37443039303038360D -->  0x37443039303038360D
0x210D               <--  0x210D

Example with the SERV type 0x1C:

MASTER PLC                    SLAVE PLC
0x3744314341484F4A31310D -->  0x3744314341484F4A31310D
0x210D                   <--  0x210D

3.1. Communication example

The RADIOSLAVE transmits the frame to the RADIOMASTER and received ACK:

15:13:17.890 rxsim   9 | S02
3744 3039 3030 3836 0D
15:13:17.891|               |7311227D 73112200|S02I   OUT    9||89 2usr  0
3744 3039 3030 3836 0D

15:13:18.189|               |73112200 7311227D|S02I    IN    2|*09 6usr  0
15:13:18.189 tx      2 | S02

The RADIOMASTER received the frame from RADIOSLAVE and transmits the ACK:

15:13:17.977|               |7311227D 73112200|S02I    IN    9|*89 2usr  0
3744 3039 3030 3836 0D
15:13:17.977 tx      9 | S02
3744 3039 3030 3836 0D

15:13:18.152 rxsim   2 | S02
15:13:18.152|               |73112200 7311227D|S02I   OUT    2||09 6usr  0

4. Configuration Parameters

(m)ode:RADIOMASTER (wired to slave)
Center (a)ddr:2200
Max (g)ap:20ms


m – RADIOMASTER – CU wired to the PLC SLAVE
s – RADIOSLAVE – CU wired to the PLC MASTER

Center (a)ddr

down part of the RADIOSLAVE MORSE address, only RADIOMASTER uses this parameter

Max (g)ap

15 to 40ms recommended, max. possible interrupting inside incomming frame on wires. After longer break is the data regarded as a new frame.


When MASTER sends the frame to the identity address 00, the the Cactus protocol in the RADIOSLAVE transmits it as broadcast. The broadcast setting must be prepared for this. It is used for network tunning purposes only.

5. History

807 – 02/2007 – protocol created

808 – 03/2007 – the parameters corrected to the state:

Cactus MASTER – CU RADIOSLAVE — CU RADIOMASTER – Cactus SLAVE – 02/2010 – (N)ACK addressed added – more on