CXD3018Q/R
§2. Subcode Interface
This section explains the subcode interface.
There are two methods for reading out a subcode externally.
The 8-bit subcodes P to W can be read from SBSO by inputting EXCK to the CXD3018Q/R.
Sub Q can be readout after checking the CRC of the 80 bits in the subcode frame.
Sub Q can be readout from the SQSO pin by inputting 80 clock pulses to the SQCK pin when SCOR comes
correctly and CRCF is high.
§2-1. P to W Subcode Readout
Data can be readout by inputting EXCK immediately after WFCK falls. (See Timing Chart 2-1.)
§2-2. 80-bit Sub Q Readout
Fig. 2-1 shows the peripheral block of the 80-bit Sub Q register.
• First, Sub Q, regenerated at one bit per frame, is input to the 80-bit serial/parallel register and the CRC check
circuit.
• 96-bit Sub Q is input, and if the CRC is OK, it is output to SQSO with CRCF = 1. In addition, 80 bits are
loaded into the parallel/serial register.
When SQSO goes high 400µs (monostable multivibrator time constant) or more after subcode readout, the
CPU determines that new data (which passed the CRC check) has been loaded.
• The CRCF reset is performed by inputting SQCK. When the subcode data is discontinuous after track jump,
etc. CRCF is reset by inputting SQCK. Then, if CRCF =1, the CPU determines that the new data has been
loaded.
• When the 80-bit data is loaded, the order of the MSB and LSB is inverted within each byte. As a result,
although the sequence of bytes is the same, the bits within the bytes are now ordered LSB first.
• Once the 80-bit data load is confirmed, SQCK is input so that the data can be read.
The SQCK input is detected, and the retriggerable monostable multivibrator is reset while the input is low.
• The retriggerable monostable multivibrator has a time constant from 270µs to 400µs. When the duration
when SQCK is high is less than this time constant, the monostable multivibrator is kept reset; during this
interval, the serial/parallel register is not loaded into the parallel/serial register.
• While the monostable multivibrator is being reset, data cannot be loaded in the 80-bit parallel/serial register.
In other words, while reading out with a clock cycle shorter than this time constant, the register will not be
rewritten by CRCOK and others. (See Timing Chart 2-2.)
• The high and low intervals for SQCK should be between 750ns and 120µs.
– 55 –
ETC [ ETC ]
