CD drive

File:Cd2 cdboard1.jpg

Top-loading drive control board.

The part that fails before everything else in CD systems. Made of a control board and an optical pickup.

The NeoGeo CD top-loading model drive was made by Sony. The CDZ one was made by Sharp ?

The control board has:

• A 4-bit mask ROM MCU (Sony CXP5084), taking care of operation sequencing and communication with the NeoGeo.
• A DSP (Sony CXD2500) to process analog data from the pickup.
• A servo controler (Sony CXA1372) to drive the pickup coils for tracking and focus.
• A spindle, sled (and tray) motor driver.

Connections

Some say the protocol was standard for the time, but clear information is hard to find. This was guessed from the system ROM disassembly, Sega MegaCD documents and a logic analyzer.

Top-loading model

Connector pinout, directions are from CDD (CD Drive) to CDC (CD Controller):

Pin #	Name	Type	Direction	Description
1	CDCK	Clock	Output	Communication clock to CDC
2	?	?	?	High ?
3	/IRQ	Signal	Output	Asks the CDC for a data exchange (low pulse at ~64Hz)
4	?	?	?	High ?
5	HOCK	Clock	Input	Communication clock from CDC
6	D0~3	Data	Both	4-bit command/status data bus
7
8
9
10	?	?	?	?
11	BCLK?	Clock	Output	Serial bit clock, should be 44100 * 32 = 1.4112MHz
12	SDATA	Data	Output	Serial data
13	LRCK	Signal	Output	I2S word clock, should be 44100Hz. Audio L/R switch for the DAC.
14	D/M ?	Signal	Output	Data/Music. Low during music playback ?
15	GND	Power	-	Ground
16	5V	Power	-	+5V for logic
17	9V	Power	-	+9V for motors and coils
18	GND	Power	-	Ground

Missing: /RESET, C2PO, and 16MHz.

Front-loading model

Connector pinout, directions are from CDD (CD Drive) to CDC (CD Controller):

Pin #	Name	Type	Direction	Description
1	SGND	Power	-	Ground
2	SVCC	Power	-
3	VCC	Power	-
4	WFCK	Clock	Output	Write Frame Clock
5	GND	Power	-	Ground
6	SCOR	Pulse	Output	Subcode sync
7	MUTE	?
8	SBSO	Data	Output	Subcode data
9	EXCK	Clock	Input	Subcode clock
10	EMP	?	?	EMPty ?
11	DOUT	Data	Output	?
12	6MHz	Clock	?	?
13	LRCK	Clock	Output	DATA L or R channel (44100Hz)
14	DATA	Data	?	Data stream
15	BCLK	Clock	Output	DATA bit clock (44100 * 24 * 2 = 2.12MHz)
16	C2PO	Data	Output	Error flag
17	DB0~3	Data	Both	4-bit command/status data bus
18
19
20
21	HOCK	Clock	Input	Communication clock from CDC
22	RESET	Pulse	Input	The name says it all
23	/IRQ	Signal	Output	Asks the CDC for a data exchange
24	L-MUTE	?
25	CDCK	Clock	Output	Communication clock to CDC

Communication

CDD to CDC communication uses a special protocol handled by the system ROM. NEO-MGA provides the I/Os through registers REG_CDDCTRL, REG_CDDINPUT, REG_CDDOUTPUT.

• The CDD regularly (~64Hz not 75) sends a low pulse on its /IRQ output to initiate a data exchange.
• HOCK goes low, indicating that the CDC aknowledges the request. The 4-bit bus direction is set to CDD to CDC.
• CDCK goes low, indicating that the CDD is starting to send its status data (A).
• HOCK goes high and the CDC reads the status data (A).
• CDCK returns high.
• HOCK returns low.
• CDCK goes low again, the B word is ready.
• The cycle continues on for 10 words...

(The delay here is not necessary, it is seen on the NeoGeo CD because of the system ROM preparing stuff).

• HOCK goes low and the 4-bit bus direction is reversed (CDC to CDD). The first command word is set (K).
• CDCK goes low, indicating that the CDD has read the data (A).
• HOCK returns high.
• CDCK returns high.
• HOCK goes low again, the B word is ready.
• The cycle continues on for 10 words...

Status data (green)

• A: Status - 1=playing, 2=seeking, 4=paused, 9=idle, 14=stopped
• B: Status
• C: Minutes high digit
• D: Minutes low digit
• E: Seconds high digit
• F: Seconds low digit
• G: Frames high digit
• H: Frames low digit
• I: Extension
• J: Checksum (see below)

Command data (red)

• K: Command
• L~S: Depends on command (see below)
• T: Checksum (see below)

Checksum

The checksum digit is the sum of all 9 previous digits, + 5, XOR 15, modulo 15: ((sum + 5) ^ 0xF) & 0xF.

Commands

See CD drive commands.

Adjustment pots

To do !