User manual

PDx-113-57/60-SE / TMCM-113-57/60-SE Firmware Manual (V1.10 / 2009-OCT-28) 13

Checksum calculation

As mentioned above, the checksum is calculated by adding up all bytes (including the module address byte)

using an 8-bit addition. Here are two examples to show how to do this:

 in C:

unsigned char i, Checksum;

unsigned char Command[9];

//Set the “Command” array to the desired command

Checksum = Command[0];

for(i=1; i<8; i++)

Checksum+=Command[i];

Command[8]=Checksum; //insert checksum as last byte of the command

//Now, send it to the module

 in Delphi:

var

i, Checksum: byte;

Command: array[0..8] of byte;

//Set the “Command” array to the desired command

//Calculate the Checksum:

Checksum:=Command[0];

for i:=1 to 7 do Checksum:=Checksum+Command[i];

Command[8]:=Checksum;

//Now, send the “Command” array (9 bytes) to the module

6.2 Reply format

Every time a command has been sent to a module, the module sends a reply.

The reply format for RS485 and RS232 is as follows:

Bytes

Meaning

Reply address

Module address

Status (e.g. 100 means “no error”)

Command number

Value (MSB first!)

Checksum

 The checksum is also calculated by adding up all the other bytes using an 8-bit addition.

 Do not send the next command before you have received the reply!