miniDSP Ltd, Hong Kong /
/ Features and specifications subject to change without prior notice
22
4.3
I2S
USAGE NOTES
Note that I2S is not a “plug and play” protocol. It requires attention to technical details such as clocking and wire
layout. It is a solution for OEMs and
advanced
DIYers (or professionals) with suitable knowledge, skills and
measurement equipment. For off-the-shelf completed units utilizing the miniSHARC board, please refer to the
Be sure to take the following precautions when designing your I2S interface and wiring:
General I2S usage notes
•
Unbuffered I2S lines must be kept short to ensure clock and data integrity.
•
If driving longer lines, buffers may be required for the clock signals (MCLK, LRCLK, and BLCK).
•
Observe correct grounding and shielding, and keep analog and digital grounds separated.
•
Ensure that the clock ratios (as listed in Table 2) are compatible with connected circuits.
3.3V logic level
All lines use a 3.3V logic level. Ensure that connected circuits use a compatible level (1.8V, for example, will
not work).
4.4
S/PDIF
CONNECTIVITY
Pins 1 and 2 of J2 are S/PDIF input and output signal lines respectively.
•
These pins cannot be connected directly to S/PDIF input or output connectors. They use a 3.3V logic
level, in contrast to the S/PDIF level of 0.5 – 0.6 V (peak to peak). A suitable level convertor circuit must
be implemented to connect to these pins.
•
Pin 1, S/PDIF input, produces the I2S data line I2S_DATA_IN3&4. This data line is accessible in the
miniSHARC_4x8
and
miniSHARC_4x8_96k
plugins as the “SPDIF” input. It is not accessible in the
OpenDRC2x2
plugin.
•
I2S_DATA_IN3&4 always has asynchronous sample rate conversion applied, from the SPDIF clock
domain to the miniSHARC’s clock domain, regardless of the I2S clock mode. The SPDIF input can
therefore be driven at any sample rate from 32 to 192 kHz.
•
Pin 2, S/PDIF output, is derived from I2S data line I2S_DATA_OUT7&8. This data line is driven as output
channels 7 and 8 in the
miniSHARC_4x8
and
miniSHARC_4x8_96k
plugins. It cannot be driven by the
OpenDRC2x2
plugin.
