<2/29> SCSP User's Manual / 1. Sound System Overview

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SCSP User's Manual / Chapter 1 Sound System Overview

1.2 Starting the sound system

■ 1. Rise from reset

The sound system can be reset by "SMPC" immediately after the power is turned on or after the reset button is pressed.
In this state, the sound CPUs "MC68EC000" and "SCSP" cannot operate.

● Reset reset

The startup of the sound system starts when "SMPC" releases the reset of "SCSP".
When the reset of the SCSP is released, the "SCSP" initializes the internal control register over a period of about 30 μs. Access is prohibited during this 30 μs period.
By the way, it is not reset by the "Reset" instruction which is the instruction of the sound CPU "MC68EC000".
In addition, the "SET" instruction cannot be used because its operation cannot be guaranteed in this system.
After 30 μs or more has passed after the reset is released, the sound block can be accessed from the main block (SH2, etc.) side.
At this point, it is finally possible to download the program and data for the sound CPU, but before that, be sure to set "1b" to the "MEM4MB" bit of the control register shown in "Table 2.1" and "DAC18B". Write "0b" to the "bit".

caution
After resetting, write "0200H" to 25B0040H.

caution	After resetting, write "0200H" to 25B0040H.

Be sure to perform this operation after resetting. Otherwise, operation cannot be guaranteed.

**Table 1.2 Initialization setting data after reset**
Main side address 25B00400 / 1h (Sound CPU side address 100400 / 1h)
address	25B00400h / 100400h								25B00401h / 100401h
bit	15	14	13	12	11	Ten	9	8	7	6	5	4	3	2	1	0
register	−						M4	D18	VER [7: 4]				MVOL [3: 0]
initial value	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0
& H (hexadecimal)	0				2				0				0

If you write the data in the above table, you will be able to access the sound RAM, so please download the program, data, waveform data, etc. for the sound CPU.
When the download is complete, cancel the sound CPU reset (sound reset) by SMPC.
When released, the sound CPU will start running according to the downloaded program. (Reset is controlled by SMPC.)

caution
The following instructions are prohibited in programming with MC68EC000.
SETET instruction
TAS command

reference:

caution	The following instructions are prohibited in programming with MC68EC000.
SETET instruction
TAS command

"SEGASATURN Developer's Information STN-51" 68000 use prohibition order

■ 2. About reset vector

Regarding the downloaded file, please do not forget that the reset vector is always required to start the sound CPU.
The reset vector is 8 bytes of data from address 0000000 on the sound RAM. See Table 2.2.

**Table 1.3 Reset Vector**
	MAIN / SOUND	D15 D8	D7 D0	MAIN / SOUND
RESET VECTOR-0	0 (2) 5A00000H / 000000H	Stack address / upper word		0 (2) 5A00001H / 000001H
	0 (2) 5A00002H / 000002H	Stack address / lower word		0 (2) 5A00003H / 000003H
RESET VECTOR-1	0 (2) 5A00004H / 000004H	Program counter / upper word		0 (2) 5A00005H / 000005H
	0 (2) 5A00006H / 000006H	Program counter / lower word		0 (2) 5A00007H / 000007H

After the reset is released, the sound CPU reads the reset vector and jumps to the same address as the value of the program counter.

The procedure for resetting is explained in Fig. 2.3 below.

Figure 2.3 Reset sequence (operation sequence diagram)

■ 3. Regarding communication between the main block and the sound block

Regarding communication between the main block and the sound block, in hardware, data is exchanged via "SCU".
Regarding access, you can read and write data from the main block (SH2, SCU) to the sound block, but please note that you cannot access the main block from the sound block.

caution Direction of access Access to the sound block is possible from the main block (SH2, SCU). Access to the main block from the sound block is not possible.

caution	Direction of access Access to the sound block is possible from the main block (SH2, SCU). Access to the main block from the sound block is not possible.

The memory mapping is the same as the one above , so please refer to that.

■ 4. About MIDI communication function

In Saturn, it is possible to use the MIDI communication function.
The serial signal line required for the MIDI interface is output to the "communication connector" on the back of Saturn.
All MIDI transmission / reception data and related controls can be performed in the SCSP control register, so when using MIDI, refer to the MIDI register section below.

reference:

"SCSP User's Manual" 4.2 Sound Source Register / ■ MIDI Register

The signal line output to the communication connector cannot be used as MIDI as it is. If you want to use it, you will need an optional device for MIDI-I / F, but there is no such product at present.

■ 5. About interrupts

The interrupt in the sound block is generated from the SCSP and can be used not only for the sound CPU but also as an interrupt for the main block (SH2).
Figure 2.4 Interrupt relationship
The interrupt of the sound CPU uses the auto vector method of MC68EC000.
For vectors, see the vector table in Table 2.2.
A total of 7 interrupt levels from 1 to 7 can be used, but since level 7 interrupts are used in the development tool, there are 6 types of interrupt levels that can be used by the user. Please note that it will be.

caution
6 levels of interrupt levels 1 to 6 that can be used by the user

caution	6 levels of interrupt levels 1 to 6 that can be used by the user

In addition, the interrupt level can be set for each interrupt factor. See the interrupt control register for details.

reference:

"SCSP User's Manual" 4.2 Sound source register / ■ Interrupt control register

caution
Interrupt level priority 7: highest ← priority → lowest: 1

Table 1.4 Interrupt vector table for sound CPU Table
Vector number address Interrupt vector content
SH2 MC68EC000
0 0 (2) 5A00000H 000000H Reset vector initial SSP value
0 (2) 5A00004H 000004H Reset vector initial PC value
:: :: :: ::
25 0 (2) 5A00064H 000064H Autovector level 1 interrupt
26 0 (2) 5A00068H 000068H Autovector level 2 interrupt
27 0 (2) 5A0006CH 00006CH Autovector level 3 interrupt
28 0 (2) 5A00070H 000070H Autovector level 4 interrupt
29 0 (2) 5A00074H 000074H Autovector level 5 interrupt
30 0 (2) 5A00078H 000078H Autovector level 6 interrupt
31 0 (2) 5A0007CH 00007CH Autovector level 7 interrupt

Reference:

caution	Interrupt level priority 7: highest ← priority → lowest: 1

**Table 1.4 Interrupt vector table for sound CPU Table**
Vector number	address	Interrupt vector content
SH2	MC68EC000
0	0 (2) 5A00000H	000000H	Reset vector initial SSP value
0 (2) 5A00004H	000004H	Reset vector initial PC value
::	::	::	::
25	0 (2) 5A00064H	000064H	Autovector level 1 interrupt
26	0 (2) 5A00068H	000068H	Autovector level 2 interrupt
27	0 (2) 5A0006CH	00006CH	Autovector level 3 interrupt
28	0 (2) 5A00070H	000070H	Autovector level 4 interrupt
29	0 (2) 5A00074H	000074H	Autovector level 5 interrupt
30	0 (2) 5A00078H	000078H	Autovector level 6 interrupt
31	0 (2) 5A0007CH	00007CH	Autovector level 7 interrupt

The SSP in the table is the supervisor stack pointer value, which is the same as the stack pointer described above.
Also, PC is the program counter value, which is also the same as above.

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