Philips SAA7345 - Manual (Page 10)

1998 Feb 16 10
Philips Semiconductors Product specification
CMOS digital decoding IC with RAM for
Compact Disc
SAA7345
B EHAVIOUR OF THE SUBQREADY-I SIGNAL
When the CRC of the Q-channel word is good, and no
subcode is being read, the SUBQREADY-I signal will react
as shown in Fig.9.
When the CRC is good and subcode is being read, the
timing in Fig.10 applies.
If t
1
(SUBQREADY-I LOW to end of subcode read) is
below 2.6 ms, then t
2
= 13.1 ms (i.e. the microcontroller
can read all subcode frames if it completes the read
operation within 2.6 ms after subcode ready).
If this criterion is not met, it is only possible to guarantee
that t
3
will be below 26.2 ms (approximately).
If subcode frames with failed CRCs are present, the t
2
and
t
3
times will be increased by 13.1 ms for each defective
subcode frame.
S HARING THE MICROCONTROLLER INTERFACE
When the RAB pin is held LOW by the microcontroller, it is
permitted to put any signal on the DA and CL lines
(SAA7345 will set output DA to high-impedance). Under
this circumstance these lines may be used for another
purpose (e.g. TDA1301 microcontroller interface Data and
Clock line, see Fig.11).
Fig.9 SUBQREADY-I timing when no subcode is read.
DA (SAA7345)
10.8 ms 15.4 ms
2.3
ms
READ start allowed
high
impedance
CRC OK CRC OK
MGA373 - 1
CL
(microcontroller)
RAB
(microcontroller)
Fig.10 SUBQREADY-I timing when subcode is being read.
Q1 Q2 Q3 Qn DA (SAA7345)
t 1
t 2
t 3
MGA374 - 1
CL
(microcontroller)
RAB
(microcontroller)