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1998 Feb 16 9
Philips Semiconductors Product specification
CMOS digital decoding IC with RAM for
Compact Disc
SAA7345
READING Q-CHANNEL SUBCODE FROM SAA7345
To read Q-channel subcode from SAA7345, the SUBQREADY-I signal should be selected as status signal. The subcode
read timing is shown in Fig.8.
Read subcode operation sequence
• Monitor SUBQREADY-I status signal.
• When this signal is LOW, and up to 2.3 ms after its LOW-to-HIGH transition, it is permitted to read subcode.
• Set CL LOW, SAA7345 will output first subcode bit (Q1).
• After subcode read starts, the microcontroller may take as long as it wants to terminate read operation.
• SAA7345 will output consecutive subcode bits after each HIGH-to-LOW transition of CL.
• When enough subcode has been read (1 to 96 bits), stop reading by pulling RAB LOW.
P
EAK DETECTOR OUTPUT
In place of the CRC-bits (bits 81 to 96), the peak detector information is added to the Q-channel data. The peak
information corresponds to the highest audio level (absolute value) and is measured on positive peaks. Only the most
significant 8 bits of the peak level are given, in unsigned notation. Bits 81 to 88 contain the LEFT peak value
(bit 88 = MSB) and bits 89 to 96 contain the RIGHT channel (bit 96 = MSB). Value is reset after reading Q-channel data.
Fig.7 SAA7345 status READ timing.
DA (SAA7345)
MGA381 - 1
STATUS
CL
(microcontroller)
RAB
(microcontroller)
DA
(microcontroller)
high impedance
Fig.8 SAA7345 Q-channel subcode READ timing.
Q1 Q2 Q3 Qn–1DA (SAA7345)
MGA382 - 1
Qn–2 Qn
STATUS
CRC
OK
CL
(microcontroller)
RAB
(microcontroller)