Chapter 1 Sound system configuration

1.1 Introduction

■1.About Sega Saturn's sound block

• The Sega Saturn's sound block consists of a CPU ``MC68000,'' a sound processing sound source IC ``SCSP (Saturn Custom Sound Processor, hereinafter referred to as SCSP),'' and 4M bits of RAM.
  (CDs can also be considered sound blocks, but I will explain them as separate.)

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

• Sound sources for Saturn include CD-DA sound sources for CDs and PCM and FM sound sources for SCSP.
  MPEG audio can also be used if 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 also possible to upgrade the sound function with various optional equipment, such as installing an expansion sound IC.
  When the optional equipment is available, I would like to see the manual for it.

• SCSP performs PCM and FM voice synthesis and voice processing.
  It has built-in sound generators for 32 units, a DSP for effect processing, a digital mixer, a timer for the sound CPU, an 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.
  This RAM can be accessed by the sound CPU (MC68EC000), SCSP, and main block (SH2, SCU).

■2.About the sound block configuration

The Sega Saturn's sound block is shown in 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”.
  The sound block assets {“ (5) SCSP” register and sound (7) RAM (4M bits)} can be accessed from the main block side and can be read and written.

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

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

• In addition, the sound block is equipped with a sound CPU (4) MC68EC000 so that it can operate independently from 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 using the main block.

●About audio line connections

• The sound block is shown in 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" on the Saturn is one stereo system, and external inputs from CD-DA, MPEG-AUDIO, and cartridge in the middle of the CD block etc. is now available for selection.

  It is also possible to apply effects to the selected input sound using 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 both from the main block such as SH2 and from MC68EC000, but please note that the addresses are different.

• Regarding the data size (byte/word/longword) for access, depending on the hardware configuration, it is more efficient to transfer in word/longword units, so when reading or writing a continuous data group, Please use words or longwords.
  Please note that byte access is prohibited 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

　Notes:

(2) of the SH-2 address is an abbreviation of +20000000H and indicates the cache-through address (Cache_through_address).

　Reference:

For information on the Sega Saturn memory map,
"HARDWARE MANUAL/SCU User's Manual" SCU mapping

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★ HARDWARE Manual ★ SCSP User's Manual

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