■3.6 CD-ROM

The CD-ROM system has an internal CPU and buffer RAM, and can operate independently from the main system. By setting conditions in advance from the main system, flexible buffer management suitable for the application structure is achieved.

●System configuration

The CD-ROM system operates simply by giving commands from the main system via the CD I/F. The sub CPU interprets commands from the main system, controls the CD-ROM drive, CDD buffer, etc., and reads data, plays videos, and plays audio. For video and audio playback, the MPEG method, which is an international standard for video compression, is adopted, and dedicated LSIs ``MPEG/Video LSI'' and ``MPEG/Audio LSI'' are used. Figure 3.29 shows the system configuration.
Sub CPU, CD buffer, frame buffer, and C/DI/F are connected to MPEG/Video. Receives compressed image data from the CD buffer and writes playback image data to the frame buffer (drawing). The drawn frame buffer data is applied with effects according to the register settings and displayed on the display device via VDP2, which controls the screen display. Alternatively, it can be transferred to the VRAM of VDP1 and VDP2 via CD I/F and SCU.
MPEG/Audio receives compressed audio data from the CD buffer and outputs stereo 1ch audio data. This audio data is output as sound via SCSP.

Figure 3.28 CD-ROM system configuration

●System specifications

Table 3.10 shows the CD-ROM system specifications, and Table 3.11 shows the CD drive specifications.

Table 3.10 CD-ROM system specifications

	Item	specification	remarks
1	G/A register width	16 bit
2	1/3 stroke average access time note	Before testing After reliability testing Double speed 500ms or less 700ms or less Standard speed 800ms or less 1000ms or less	Average value of the time measured 200 times (100 round trips) from when the CD drive receives the PLAY command until it issues the PLAY status.
3	Rotational speed	Normal: 620~1680rpm Double speed: 1240~3360rpm
4	CD read speed	Normal speed: 75 sectors/sec = 150KB/sec 2x speed: 150 sectors/sec = 300KB/sec
5	Tray opening/closing method	top loading
6	Memory capacity	RAM 512KB (for CD buffer) ROM 64KB (for BIOS) RAM512KB (for MPEG)
7	data transfer rate	Maximum 8MB/sec, maximum 4MB/sec during MPEG operation
8	LED	Flashes depending on the CD operating status.

note

• 1/3 stroke is from 15 minutes 00 seconds 00 frames to 35 minutes 00 seconds 00 frames.
• The above values are for reference only and do not guarantee operation.

Table 3.11 CD drive specifications

	Item	specification	remarks
1	CD playback	Specified track/index playback Frame address (corresponds to absolute time) specified playback Resume playback (cancel pause, control pickup movement) repeat play CD-DA and CD-ROM can be controlled with the same command format scan playback Get subcode
2	others	Multi-session compatible Emphasis compatible Decoding and error correction compatible with CD-ROM XA (Subheader recognition, ECC processing, read retry processing)

●Function

The main features of the CD-ROM system are listed below.

• Stream selection
• Parallel processing
• MPEG function
• Compatible standards

The CD-ROM system temporarily stores data read from the CD-ROM in the CD buffer. The stored data is written to and read from MPEG and the main system according to commands from the main system.
Figure 3.29 shows the data flow of the CD-ROM system.

Figure 3.29 Data flow in CD-ROM system

●Stream selection
The flow of data from the CD-ROM is called a stream. Streams include audio data, video data, and program data. The stream selection mechanism selects the data type and sends the data to the main system and MPEG (Figure 3.30). The control contents of the stream selection mechanism are shown below.

• Stream data is accumulated in the CD buffer and selected according to the data type.
• Data from devices such as CD-ROM and MPEG decoders are controlled in a unified manner.
• Set stream selection conditions using commands.

Figure 3.30 Stream selection mechanism

●Parallel processing
The CD-ROM system operates independently of the main system to read streams, select streams, and control the CD drive. Furthermore, multiple stream selection mechanisms are set up, allowing parallel processing.

●MPEG function
MPEG plays videos with audio.
Before playback, image data is compressed to approximately 1/50 and audio data to approximately 1/10, so 74 minutes can be recorded on a CD. In addition, since playback is performed using a dedicated LSI, there is no burden on the CPU, allowing you to play games while playing high-quality videos.

◆MPEG/Video functions
Saturn's MPEG/Video is equipped with various special functions customized exclusively for Saturn.

• Window function
  As shown in Figure 3.31, this function cuts out a portion of the played image and displays it on the TV screen at any size. By using this function, you can ``change the display position and display size of the MPEG playback image'', ``select and display one of multiple screens'', ``zoom in and out'', etc.

  Figure 3.31 Window function
  

• Interpolation function
  MPEG playback images have a maximum resolution of 352 x 240 dots, but can be displayed at a maximum resolution of 704 x 480 dots using horizontal and vertical interpolation, resulting in smooth display with minimal flickering.

• Blur function
  The blur function is a function that displays the average of the color data of 4 horizontally and vertically adjacent dots, and can create an effect that blurs distant backgrounds.

• Mosaic function
  Divide the MPEG playback image horizontally and vertically into specified sizes, and display the color of the upper left dot of each area for all dots in that area. You can specify up to full screen size independently horizontally and vertically.

  Figure 3.32 Interpolation, blurring, and mosaic functions
  

• Fade function
  This is a function that applies magnification to the screen brightness and color difference signals and displays them, and is used for fade-ins, fade-outs, etc. Since this method does not add or subtract the offset value, only the brightness can be changed correctly. Also, by changing the color difference signal, you can display monochrome images or make the displayed colors darker.

• Chromakey function
  This is a function that plays videos with transparent dots, as shown in Figure 3.33. Chromakey is a method in which ``a person is photographed in front of a blue wall, and the non-blue parts are extracted from that image and superimposed on another picture.'' With existing MPEG LSIs, MPEG video images can only be used in the background, but with Saturn's chroma key function, MPEG video images can be displayed overlaid on sprites and scrolls.

  Figure 3.33 Chromakey function
  

• Screen capture function
  This function imports video played in MPEG to the main system. This function allows you to treat video images played in MPEG as sprites, use them as texture data, display them with VDP1 and VDP2 functions, and even play multiple videos.
  The amount of data in an MPEG video is 50 times the amount of data from a CD, and the transfer speed is faster than that from a CD buffer, so it can also be used for high-speed rewriting of texture data.

• High-definition static function
  This function displays high-definition still images of 704 dots x 480 dots. Full-color high-definition images cannot be displayed on the main system (up to 352 x 240 dots in full color), but by using the high-definition still image function, you can display images with the maximum number of colors on the Saturn.

• Pause function, freeze function
  The pause function is a function that freezes the video at any frame, allowing slow playback and frame-by-frame playback.
  The freeze function is a function that stores video in arbitrary frames (image memory) and allows strobe playback.

• Branch playback function
  With MPEG, compressed image data can be stored in the CD buffer memory, so videos can be played even during CD seek (track search). Therefore, even if you jump to a video on a different track, the video will continue to play instead of becoming a static screen like an LD. The branch playback function enables MPEG to perform branch playback where the branch point cannot be determined. You can also "loop play" the same video over and over again.

◆MPEG/Audio functions

Audio data played in MPEG/Audio is sent to SCSP through the same route as CD-DA (music CD), and various effects can be applied to it.

• Compression rate variable
  You can choose the compression rate depending on your application, and you can choose from 1/3.5 to 1/21 compression. Using 1/21 compression, you can record 50 hours of audio on a CD. Even in long RPGs and ADVs, all lines and narration can be done by voice.

• On-memory playback function
  MPEG/Audio can be compressed from 1/3.5 to 1/21. For example, if you use 1/21 compression and use half of the 4M bits of CD buffer memory for MPEG/Audio, you can easily access the CD. You can play 64 seconds of audio without having to do anything. This allows audio playback without waiting time. You can also connect short lines to create longer conversations.

●Compatible standards
Table 3.12 shows the standards supported by the CD-ROM system.

 Standard

 explanation

 CD-DA

 This is the standard name for the sound contained in CDs, and is based on the RED BOOK international standard.
 Sampling frequency 44.1KHz, quantization bit 16 bit stereo.

 CD-G,CD-EG

 Data such as graphics is recorded in the format area of the music CD.
 Adopts 16 display colors and CD-DA sound quality.

 CD-ROM

 Computer data can be recorded in the same physical format as music CDs (CD-DA).
 This is a standard established by Based on the YELLOW BOOK international standard.

 CD-ROM XA

 Expands CD-ROM to allow interleaved recording for parallel playback of images and audio.
 This is a powerful recording format.

 E.B.
 (E-book)

 CD-ROM software adopted by Sony's e-book player "Data Discman"
 recording format.

 Photo-CD

 This is a system that allows you to view photos on a monitor such as a TV.
 Up to 100 photos can be recorded on a CD, and the same photo can be enlarged or reduced.

 Video CD
 (KARAOKE CD)

 Contains video compressed by MPEG. Up to 74 minutes can be recorded on a CD with high precision.
 Up to 2000 detailed still images can be played back.