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 check sum 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

<Example1> Setting PERCUSSION SWITCH to ON (DT1)

According to the “Parameter Address Map” (p. 109), the start address of “Temporary Registration” is 10 00 00 00H, the offset address of “Registration Organ” parameter is 00 02 00H, and the address of “Percussion Switch” is 00 09H. Therefore the address of “Percussion Switch” of Registration is;

10 00 00 00H

00 02 00H

+) 00 09H 10 00 02 09H

ON has the value of 01H.

So the system exclusive message should be sent is;

 

 

 

F0

41

10

00 5F

12

10 00 02 09

01

??

F7

(1)

(2)

(3)

(4)

(5)

address

data

checksum

(6)

(1) Exclusive Status

 

(2) ID (Roland)

(3) Device ID (17)

(4) Model ID (VR-760)

 

(5) Command ID (DT1)

(6) End of Exclusive

Then calculate the checksum.

10H + 00H + 02H + 09H + 01H = 16 + 0 + 2 + 9 + 1 = 28 (sum) 28 (sum) ÷ 128 = 0 (quotient) ... 28 (remainder)

checksum = 128 - 28 (remainder) = 100 = 64H

This means that F0 41 10 00 5F 12 10 00 02 09 01 64 F7 is the message should be sent.

<Example2> Getting Temporary Performance data (RQ1)

cf.) This operation is the same as Bulk Dump Temporary function in Utility.

According to the “Parameter Address Map” (p. 109), the start address of Temporary Registration is assigned as following:

10 00

00

00H

Temporary Registration

 

:

 

 

00

00

00H

Registrartion Common

 

:

 

 

00

02

00H

Registration Organ

 

:

 

 

00

04

00H

Registration Piano

 

:

 

 

00

06

00H

Registration Synth

 

:

 

 

10 00

?? ??H

End of Temporary Registration

As the data size of “Registration Synth” is 00 00 01 1DH, summation of the size and the start address of “Registration Synth” at “Temporary Registration” will be;

10 00 06 00H +) 00 00 01 1DH 10 00 07 1DH

And the size that have to be got should be;

10 00 07 1DH -) 10 00 00 00H 00 00 07 1DH

Therefore the system exclusive message should be sent is;

 

 

F0

41

10

00 5F

11

10 00 00 00

00 00 07 1D ??

F7

(1)

(2)

(3)

(4)

(5)

address

data

checksum

(6)

(1) Exclusive Status

 

(2) ID (Roland)

 

(3) Device ID (17)

 

(4) Model ID (VR-760)

 

(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 5F 11 10 00 00 00 00 00 07 1D 4C to be transmitted.

ASCII Code Table

Registration Name of MIDI data are described the ASCII code in the table below.

+————————————————————————————————————————————————————————————————+ D H Char D H Char D H Char ——————+——————+——————++——————+——————+——————++——————+——————+——————

32

20H

SP

64

40H

@

96

60H

`

33

21H

!

65

41H

A

97

61H

a

34

22H

66

42H

B

98

62H

b

35

23H

#

67

43H

C

99

63H

c

36

24H

$

68

44H

D

100

64H

d

37

25H

%

69

45H

E

101

65H

e

38

26H

&

70

46H

F

102

66H

f

39

27H

`

71

47H

G

103

67H

g

40

28H

(

72

48H

H

104

68H

h

41

29H

)

73

49H

I

105

69H

i

42

2AH

*

74

4AH

J

106

6AH

j

43

2BH

+

75

4BH

K

107

6BH

k

44

2CH

,

76

4CH

L

108

6CH

l

45

2DH

77

4DH

M

109

6DH

m

46

2EH

.

78

4EH

N

110

6EH

n

47

2FH

/

79

4FH

O

111

6FH

o

48

30H

0

80

50H

P

112

70H

p

49

31H

1

81

51H

Q

113

71H

q

50

32H

2

82

52H

R

114

72H

r

51

33H

3

83

53H

S

115

73H

s

52

34H

4

84

54H

T

116

74H

t

53

35H

5

85

55H

U

117

75H

u

54

36H

6

86

56H

V

118

76H

v

55

37H

7

87

57H

W

119

77H

w

56

38H

8

88

58H

X

120

78H

x

57

39H

9

89

59H

Y

121

79H

y

58

3AH

:

90

5AH

Z

122

7AH

z

59

3BH

;

91

5BH

[

123

7BH

{

60

3CH

<

92

5CH

\

124

7CH

61

3DH

=

93

5DH

]

125

7DH

}

62

3EH

>

94

5EH

^

 

 

 

63

3FH

?

95

5FH

_

 

 

 

+————————————————————————————————————————————————————————————————+ D: decimal

H:hexadecimal

“SP” is space.

112

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Image 112
Roland VR-760 112, Example of an Exclusive Message Calculating a Checksum, Ascii Code Table, How to calculate the checksum

VR-760 specifications

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