CookTek MCD3000 Specifications download pdf (Page 16)

MCD3000 Series

MG.15.A4.22 - VLT is a registered Danfoss trademark 15

Installation

these parameters are uploaded to the MCD3000 there

will be no effect and no error generated.

■ Serial communications – calculating the

check sum (LRC)

Each command string sent to and from the MCD3000

includes a check sum. The form used is the

Longitudinal Redundancy Check (LRC) in ASCII hex.

This is an 8-bit binary number represented and

transmitted as two ASCII hexadecimal characters.

To calculate LRC:

1. Sum all ASCII bytes

2. Mod 256

3. 2’s complement

4. ASCII convert

For example Command String (Start);

ASCII STX B 1 0

or 02h 42h 31h 30h

ASCII Hex Binary

STX 02h 0000 0010

B 42h 0100 0010

1 31h 0011 0001

0 30h 0011 0000

A5h 1010 0101 SUM (1)

A5h 1010 0101 MOD 256 (2)

5Ah 0101 1010 1’s COMPLEMENT

01h 0101 1011 + 1 =

5Bh 0101 1011

2’s COMPLEMENT (3)

ASCII 5 B ASCII CONVERT (4)

or 35h 42h LRC CHECKSUM

The complete command string becomes

ASCII STX B 1 0 5 B ETX

or 02h 42h 31h 30h 35h 42h 03h

To verify a received message containing an LRC;

1. Convert last two bytes of message from ASCII to

binary.

2. Left shift 2

to last byte 4 bits.

3. Add to last byte to get binary LRC.

4. Remove last two bytes from message.

5. Add remaining bytes of message.

6. Add binary LRC.

7. Round to one byte.

8. The result should be zero.

Response or status bytes are sent from the MCD3000

as an ASCII string.

STX [d1]h [d2]h [d3]h [d4]h LRC1 LRC2 ETX

d1 = 30h

d2 = 30h

d3 = 30h plus upper nibble of status byte right

shifted by four binary places.

d4 = 30h plus lower nibble of status byte.

For example status byte = 1Fh, response is

STX 30h 30h 31h 46h LRC1 LRC2 ETX

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 49 50

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CookTek MCD3000 Specifications Page 16

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