Chapter 1 Sound system configuration

1.1 Introduction

■ 1. About the sound block of Sega Saturn

• The Sega Saturn sound block consists of a CPU "MC68000", a sound processing sound source IC "SCSP (Saturn Custom Sound Progressor, hereinafter SCSP)", and a 4M-bit RAM.
  (You can think of a CD as a sound block, but I'll explain it as a separate one.)

• Since the sound block itself has a CPU, it can operate independently of the main system (SH2, etc.).
  This can reduce the processing load on the main CPU side including SH2.
  The sound CPU is responsible for controlling the entire sound block, including the SCSP.

• Sound sources in Saturn include CD-DA sound sources of CDs and PCM and FM sound sources by SCSP.
  In addition, MPEG audio can also be used when an optional device for VIDEO-CD is connected.
  (However, please note that CD-DA and MPEG audio cannot be used at the same time.)

  In addition, by using the digital audio input from the cartridge connector, it is possible to upgrade the sound function with various optional devices such as installing an extended sound IC.
  If you have an optional device, I hope you will see it in the manual.

• SCSP performs PCM and FM speech synthesis and speech processing.
  It has 32 sound generators, DSP for effect processing, digital mixer, timer for sound CPU, interrupt controller, etc.

• The sound RAM is equipped with 4M bits (512K bytes).
  This memory is used for sound CPU programs, data and waveform data, delay buffers for effects, etc.
  The sound CPU (MC68EC000), SCSP, and main block (SH2, SCU) can access this RAM.

■ 2. About sound block configuration

The Sega Saturn sound block looks like Figure 1.1.

Figure 1.1 Sound block

● Relationship between main block and sound block

• The sound block is connected to the main block via “(1) SCU”.
  Sound block assets {“ (5) SCSP” registers and sound (7) RAM (4M bits)} are accessible from the main block side and can be read and written.

  * Please note that some registers have restrictions such as "read only" and "write only".

• On the contrary, please note that the sound CPU cannot access the memory etc. on the main block side.

• Moreover, the sound block is equipped with "(4) MC68EC000" as a sound CPU so that it can operate independently of the main block.

  By installing this CPU, it is possible to remove the sound block control burden from the main block side.

  * Of course, it is also possible to control the sound block by the main block.

● About audio line connection

• The sound block looks like Figure 1.1, and basically all audio signals are collected in the sound block (SCSP).
  

  Regarding the output from each sound source, the number of sound sources that can be input to "SCSP" in Saturn is one stereo system, and CD-DA, MPEG-AUDIO, and external input from the cartridge in the middle CD block etc. Is to be selected.

  It is also possible to apply an effect to the selected and input sound with the DSP in "SCSP".

● Sound memory map

• The memory and registers of the sound block are arranged as shown in Figure 1.2.
  Basically, it can be accessed from both the main block such as SH2 and from MC68EC000, but please note that the address is different.

• Regarding the data size (byte / word / long word) for access, transfer in word / long word units is more efficient depending on the hardware configuration, so when reading or writing continuous data groups, Please use word or long word units.
  Please note that byte access is prohibited for access from the main side including SH2.

Table 1.1 Sound memory mapping (overview)

		D15 ~ D8	D7 ~ D0
SH2-ADDRESS	MC68EC000-ADDRESS	UPPER	LOWER	MC68EC000-ADDRESS	SH2-ADDRESS
0 (2) 5A00000H	000000H	Sound RAM 512K bytes		000001H	0 (2) 5A00001H
:: :: :: :: ::	:: :: :: :: ::			:: :: :: :: ::	:: :: :: :: ::
0 (2) 5A7FFFEH	07FFFEH			07FFFFH	0 (2) 5A7FFFFH
:: :: :: :: ::	:: :: :: :: ::	:: :: :: :: ::		:: :: :: :: ::	:: :: :: :: ::
0 (2) 5B00000H	100000H	Control register		100001H	0 (2) 5B00001H
:: ::	:: ::			:: ::	:: ::
0 (2) 5B00EE2H	100EE2H			100EE3H	0 (2) 5B00EE3H

Note:

SH-2 address (2) is an abbreviation of + 20000000H and indicates a cash-through address (Cashe_through_address).

reference:

For the memory map of Sega Saturn,
"HARDWARE MANUAL / SCU User's Manual" SCU Mapping