Designer Systems pHAT-HIFI, Technical Description

Page: 18 / 20

pHAT Module Series
pHAT-HIFI Technical Description
pHAT-HIFI Technical Description
Page 18 of 20
6 References
6.1 I
2
S protocol
Figure 2: I
2
S protocol
Serial data is transmitted in two’s complement with the MSB first. The MSB is transmitted first
because the transmitter and receiver may have different word lengths. It isn’t necessary for
the transmitter to know how many bits the receiver can handle, nor does the receiver need to
know how many bits are being transmitted.
When the system word length is greater than the transmitter word length, the word is
truncated (least significant data bits are set to ‘0’) for data transmission. If the receiver is sent
more bits than its word length, the bits after the LSB are ignored. On the other hand, if the
receiver is sent fewer bits than its word length, the missing bits are set to zero internally. And
so, the MSB has a fixed position, whereas the position of the LSB depends on the word length.
The transmitter always sends the MSB of the next word one clock period after the WS
changes.
Serial data sent by the transmitter may be synchronized with either the trailing (HIGH-to-
LOW) or the leading (LOW-to-HIGH) edge of the clock signal. However, the serial data must be
latched into the receiver on the leading edge of the serial clock signal, and so there are some
restrictions when transmitting data that is synchronized with the leading edge.