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General notes

The purpose of the interface is to allow a computer to control all S900/S950 functions, to process and synthesize samples, and to allow the S950 to replay samples developed for other samplers, e.g., the Prophet 2000.

The S950 is always a slave; it will never send unless it is told to. This means all data transfers out of the S950 must use two-way communication. The S950 can however receive with an incoming connection only. Reception of sample dump is speeded up with a two-way connection.

Programs and samples are requested by number. In the case of programs this will correspond to the number on the PLAY menu decreased by one. For samples the number will be the order in which they are in the S950's RAM. The program/name catalog sent by the S950 has a number against each name, starting with 0.

When the S950 receives a sample, the name it shows will be that number. Programs are received with an alphanumeric name.

Sample transfer is according to the standard described in the Prophet 2000 manual. This uses system exclusive common which does not include a manufacturer's prefix code. As it does not include a MIDI channel code, any samples sent, or request for samples would be responded to by all samplers on the same MIDI line. The system exclusive common reception enable and disable messages--which DO include a MIDI channel number--can be used to select one of several S950's on the same line.

A further enhancement of the standard sample dump protocol is that when closed loop transmission is used, gaps between blocks may be as long as 10 seconds rather than the 20 msec specified. This allows the computer to use its disk in the middle of a long file. This variation maintains full compatibility with the standard.

There are several parameters associated with an S950 sample that are not included in the Prophet 2000 sample dump. These may be sent with the Akai exclusive sample parameters messages.

The use of the above enhancements will not prevent the S950 from being completely compatible with the Prophet 2000 sample dump format.

The machine code execution facility allows the operating system within the S950's memory to be altered by MIDI messages.

History:

Coding of DB DW DD SW

Signed and unsigned

Parameters described as signed are represented in two's complement form, e.g., DB value of -1 equals 0FFh.

ASCII characters

Where a value is shown as a character in single quotes it is in ASCII form with the MSB=0, e.g., 'A' equals 41h.

Undefined and reserved

Reserved values are for possible future enhancements and must be transmitted as shown. Undefined values have no operational effect and might as well be filled with 0s.

Time out

When receiving Akai exclusive data, after the first six bytes have been received, the remaining bytes must be separated by no more than 2 seconds. This provision protects the S950 from hanging in the event of incomplete messages.

RS232-C

The S950 can receive either through MIDI or through RS232-C. The switch from one to the other can be made manually (page 5 of the MIDI menu), or by Akai exclusive overall settings reception, or if an entire disk is loaded on which the overall settings was saved. (This is done automatically when entire memory is saved.)

Specification for RS232-C:

Connector 25 pin "D". S950 is female.
Levels High +3V to +15V, low -3V to -15V.
Bits 8
Parity none
Stop bits 1
Baud rate 300, 600, 1200, 2400, 4800, 9600, and 19200. Also many non-standard rates up to 100000. The default baud rate is 9600; transmission at higher rates than 19200 should use a short cable.
Protocol Hardware handshake using CTS/RTS. Handshake need not be used on rates below 50000 baud, in which case RTS should be tied high.

The S950 is configured as DCE and should be connected to most computers with a non-switching cable with the following pin connections:

Pin S950 Computer
1 FG FG Frame ground
2 RXD TXD Data in to S950
3 TXD RXD Data out of S950
4 CTS RTS Clear to send
5 RTS CTS Request to send
7 GND GND Signal ground