MIDI Implementation

Example of an Exclusive Message and

Calculating a Checksum

Roland Exclusive messages (RQ1, DT1) are transmitted with a checksum at the end (before F7) to make sure that the message was correctly received. The value of the checksum is determined by the address and data (or size) of the transmitted Exclusive message.

How to calculate the checksum

(hexadecimal numbers are indicated by “H”)

The checksum is a value derived by adding the address, size, and checksum itself and inverting the lower 7 bits.

Here's an example of how the checksum is calculated. We will assume that in the Exclusive message we are transmitting, the address is aa bb cc ddH and the data or size is ee ffH.

aa+ bb + cc + dd + ee + ff = sum sum ÷ 128 = quotient ... remainder 128 - remainder = checksum

<Example 1> Setting CHORUS TYPE of PERFORMANCE COMMON to DELAY (DT1)

According to the “Parameter Address Map” (p. 279), the start address of Temporary Performance is 10 00 00 00H, the offset address of CHORUS at PERFORMANCE COMMON is 04 00H, and the address of CHORUS TYPE is 00 00H. Therefore the address of CHORUS TYPE of PERFORMANCE COMMON is;

10 00 00 00H

04 00H

+) 00 00H 10 00 04 00H

DELAY has the value of 02H.

So the system exclusive message should be sent is;

F0

41

10

00 10

12

10 00 04 00

02

??

F7

(1)

(2)

(3)

(4)

(5)

address

data

checksum

(6)

(1) Exclusive Status

(2) ID (Roland)

 

(3) Device ID (17)

 

(4) Model ID (XV-88)

(5) Command ID (DT1)

(6) End of Exclusive

 

Then calculate the checksum.

10H + 00H + 04H + 00H + 02H = 16 + 0 + 4 + 0 + 2 = 22 (sum) 22 (sum) ÷ 128 = 0 (quotient) ... 22 (remainder)

checksum = 128 - 22 (remainder) = 106 = 6AH

This means that F0 41 10 00 10 12 10 00 04 00 02 6A F7 is the message should be sent.

<Example 2> Getting the data (RQ1) of Performance Part 3 in USER:03

According to the “Parameter Address Map” (p. 279), the start address of USER:03 is 20 02 00 00H, and the offset address of Performance Part 3 is 00 22 00H.

Therefore the start address of Performance Part 3 in USER:03 is;

20 02 00 00H

+) 00 22 00H 20 02 22 00H

As the size of Performance Part is 00 00 00 21H, the system exclusive message should be sent is;

F0

41

10

00 10

11

20 02 22 00

00 00 00 21

??

F7

(1)

(2)

(3)

(4)

(5)

address

data

checksum

(6)

(1) Exclusive Status

(2) ID (Roland)

 

(3) Device ID (17)

 

(4) Model ID (XV-88)

(5) Command ID (RQ1)

(6) End of Exclusive

 

Then calculate the checksum.

20H + 02H + 22H + 00H + 00H + 00H + 00H + 21H = 32 + 2 + 34 + 0 + 0 + 0 + 0 + 33 = 101 (sum)

101 (sum) ÷ 128 = 0 (quotient) ... 101 (remainder) checksum = 128 - 101 (remainder) = 27 = 1BH

This means that F0 41 10 00 10 11 20 02 22 00 00 00 00 21 1B F7 is the message should be sent.

<Example 3> Getting Temporary Performance data (RQ1)

cf.) This operation is the same as Data Transfer function in Utility mode with “PERFORM” (Type parameter) and “TEMP: -PATCH” (Source parameter) options.

According to the “Parameter Address Map” (p. 279), the start address of Temporary Performance is assigned as following:

10 00 00 00H

Temporary Performance Common

:

 

10 00 20 00H

Temporary Performance Part 1

:

 

10 00 2F 00H

Temporary Performance Part 16

As the data size of Performance Part is 00 00 00 21H, summation of the size and the start address of Part 16 at Temporary Performance will be;

10 00 2F 00H +) 00 00 00 21H 10 00 2F 21H

And the size that have to be got should be;

10 00 2F 21H -) 10 00 00 00H 00 00 2F 21H

Therefore the system exclusive message should be sent is;

F0

41

10

00 10

11

10 00 00 00

00 00 2F 21

??

F7

(1)(2)

(3)

(4)

(5)

address

data

checksum

(6)

 

(1) Exclusive Status

(2) ID (Roland)

 

(3) Device ID (17)

 

 

(4) Model ID (XV-88)

(5) Command ID (RQ1)

(6) End of Exclusive

 

Calculating the checksum as shown in <Example 2>, we get a message of F0 41 10 00 10 11 10 00 00 00 00 00 2F 21 20 F7 to be transmitted.

<Example 4> Getting data (RQ1) at once; Temporary Performance data,

Temporary Patch data of whole part in Performance mode,

Temporary Rhythm data of whole part in Performance mode.

cf.) This operation is the same as Data Transfer function in Utility mode with “PERFORM” (Type parameter) and “TEMP: +PATCH” (Source parameter) options.

According to the “Parameter Address Map” (p. 279), the start address of the above all parameters is assigned as following:

10 00 00 00H

Temporary Performance

11 20 00 00H

Temporary Patch (Performance Mode Part 1)

11 30 00 00H

Temporary Rhythm (Performance Mode Part 1)

:

 

14 60 00 00H

Temporary Patch (Performance Mode Part 16)

14 70 00 00H

Temporary Rhythm (Performance Mode Part 16)

The offset address of Rhythm is also assigned as follows:

00 00 00H

Rhythm Common

:

 

 

00 10 00H

Rhythm Tone 1

:

 

 

01 3E

00H

Rhythm Tone 4

As the data size of Rhythm Tone is 00 00 01 41H, summation of the size and the start address of Tone 4 of Part 16 at Temporary Patch in Performance mode will be;

14 70 00 00H

01 3E 00H +) 00 00 01 41H 14 71 3F 41H

And the size that have to be got should be;

14 71 3F 41H -) 10 00 00 00H 04 71 3F 41H

Therefore the system exclusive message should be sent is;

F0

41

10

00 10

11

10 00 00 00

04 71 3F 41

??

F7

(1)

(2)

(3)

(4)

(5)

address

data

checksum

(6)

(1) Exclusive Status

(2) ID (Roland)

 

(3) Device ID (17)

 

(4) Model ID (XV-88)

(5) Command ID (RQ1)

(6) End of Exclusive

 

Calculating the checksum as shown in <Example 2>, we get a message of F0 41 10 00 10 11 10 00 00 00 04 71 3F 41 7B F7 to be transmitted.

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Roland XV-88 owner manual 294, Example of an Exclusive Message Calculating a Checksum