Roland VR-760 - Manual (Page 112)

112
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.