Roland RD-700 owner manual 160, Examples of Actual Midi Messages, How to calculate the checksum

MIDI Implementation

■Examples of Actual MIDI Messages

<Example1> 92 3E 5F

9n is the Note-on status, and n is the MIDI channel number. Since 2H = 2, 3EH = 62, and 5FH = 95, this is a Note-on message with MIDI CH = 3, note number 62 (note name is D4), and velocity 95.

<Example2> CE 49

CnH is the Program Change status, and n is the MIDI channel number. Since EH = 14 and 49H = 73, this is a Program Change message with MIDI CH = 15, program number 74 (Flute in GS).

<Example3> EA 00 28

EnH is the Pitch Bend Change status, and n is the MIDI channel number. The 2nd byte (00H

=0) is the LSB and the 3rd byte (28H = 40) is the MSB, but Pitch Bend Value is a signed number in which 40 00H (= 64 x 12+80 = 8192) is 0, so this Pitch Bend Value is

28 00H - 40 00H = 40 x 12+80 - (64 x 12+80) = 5120 - 8192 = -3072

If the Pitch Bend Sensitivity is set to 2 semitones, -8192 (00 00H) will cause the pitch to change -200 cents, so in this case -200 x (-3072) ÷ (-8192) = -75 cents of Pitch Bend is being applied to MIDI channel 11.

<Example4> B3 64 00 65 00 06 0C 26 00 64 7F 65 7F

BnH is the Control Change status, and n is the MIDI channel number. For Control Changes, the 2nd byte is the control number, and the 3rd byte is the value. In a case in which two or more messages consecutive messages have the same status, MIDI has a provision called “running status” which allows the status byte of the second and following messages to be omitted. Thus, the above messages have the following meaning.

B3	64	00	MIDI ch.4, lower byte of RPN parameter number:	00H
(B3)	65	00	(MIDI ch.4) upper byte of RPN parameter number:	00H
(B3)	06	0C	(MIDI ch.4) upper byte of parameter value:	0CH
(B3)	26	00	(MIDI ch.4) lower byte of parameter value:	00H
(B3)	64	7F	(MIDI ch.4) lower byte of RPN parameter number:	7FH
(B3)	65	7F	(MIDI ch.4) upper byte of RPN parameter number:	7FH

In other words, the above messages specify a value of 0C 00H for RPN parameter number 00 00H on MIDI channel 4, and then set the RPN parameter number to 7F 7FH.

RPN parameter number 00 00H is Pitch Bend Sensitivity, and the MSB of the value indicates semitone units, so a value of 0CH = 12 sets the maximum pitch bend range to ±12 semitones (1 octave). (On GS sound generators the LSB of Pitch Bend Sensitivity is ignored, but the LSB should be transmitted anyway (with a value of 0) so that operation will be correct on any device.)

Once the parameter number has been specified for RPN or NRPN, all Data Entry messages transmitted on that same channel will be valid, so after the desired value has been transmitted, it is a good idea to set the parameter number to 7F 7FH to prevent accidents. This is the reason for the (B3) 64 7F (B3) 65 7F at the end.

It is not desirable for Performance data (such as Standard MIDI File data) to contain many events with running status as given in <Example 4>. This is because if playback is halted during the song and then rewound or fast-forwarded, the sequencer may not be able to transmit the correct status, and the sound generator will then misinterpret the data. Take care to give each event its own status.

It is also necessary that the RPN or NRPN parameter number setting and the value setting be done in the proper order. On some sequencers, events occurring in the same (or consecutive) clock may be transmitted in an order different than the order in which they were received. For this reason it is a good idea to slightly skew the time of each event (about 1 tick for TPQN = 96, and about 5 ticks for TPQN = 480).

*TPQN: Ticks Per Quarter Note

Appendices

■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 CHORUS TYPE to DELAY (DT1)

According to the “Parameter Address Map” (p. 153), the start address of Temporary Setup is 10 00 00 00H, the offset address of CHORUS at Setup is 04 00H, and the address of CHORUS TYPE is 00 00H. Therefore the address of CHORUS TYPE of Setup 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	43	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 (RD-700)				(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 43 12 10 00 04 00 02 6A 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. 153), the start address of Temporary Setup is assigned as following:

10 00 00 00H	Setup Common
	:
10 00 69 00H	Setup Tone Wheel 10 Backup

As the data size of Setup Tone Wheel Back up is 00 00 00 0BH, summation of the size and the start address of Setup Tone Wheel 10 Back up at Temporary Setup will be;

10 00 69 00H

+) 00 00 00 0BH

10 00 69 0BH

And the size that have to be got should be;

10 00 69 0BH

-) 10 00 00 00H

00 00 69 0BH

Therefore the system exclusive message should be sent is;
F0	41	10	00 43	11	10 00 00 00	00 00 69 0B	??	F7
(1)	(2)	(3)	(4)	(5)	address	data	checksum	(6)
(1) Exclusive Status				(2) ID (Roland)		(3) Device ID (17)
(4) Model ID (RD-700)				(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 43 11 10 00 00 00 00 00 69 0B 7C to be transmitted.

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