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I
2
S Converter
LH79524/LH79525 User’s Guide
10-4
Version 1.0
The I
2
S converter operates in both Master and Slave Modes. In Master Mode, the clock
and word select inputs (SSPCLKOUT and SSPFSSOUT) are supplied by the SSP block.
In slave mode, the clock and word select inputs are supplied by the external CODEC via
the PB3/SSPCLK/I2SCLK and PB2/SSPFRM/I2SWS pins.
The I
2
S Converter requires the SSP to be enabled and operating in continuous mode. It is
also required that the SSP operate in full duplex mode (SOD = 0) while the I
2
S Converter
is enabled. The SOD allows the SSP to operate in receive-only mode which may result in
a condition where the channel indicated by the TXFIFO (left or right) may differ from the
channel indicated by the RXFIFO. The I
2
S Converter requires the FIFOs to be in sync with
respect to which channel each is expecting. If the FIFOs become out of sync, then the
behavior of the I
2
S may be unpredictable. For this reason, I
2
S is not compatible with
receive-only mode of the SSP.
The SSPOE_n signal from the SSP is altered by the I
2
S Converter to enable the transmit
data pad whenever the I
2
S is enabled. If the I
2
S Converter is disabled, then the output
enable passes unchanged through the I
2
S Converter.
10.1.2 Driving/Latching Edges
The SSP and any device connected to it is expected to drive data and the frame pulse
on the rising edge of the clock and latch both on the falling edge of the clock. The I
2
S Spec-
ification states that the I
2
S Converter may drive data and the word strobe on either edge
of the clock but both are always latched on the rising edge of the clock.
Therefore, the data and frame pulse received by the I
2
S from the SSP are sampled on the
falling edge of the clock and moved to the rising edge of the clock. The data and word
strobe received by the I
2
S at the pins of the chip are sampled on the rising edge of the
clock. If the I
2
S Converter is disabled, the SSP data and frame pulse are passed through
without being altered by the I
2
S.
Figure 10-4. Driving/Latching Diagram
LH79525-87
SSPFSSIN
SSPCLKOUT
SSPRXD
SSPCLKIN
SSPFSSIN
SSPRXD
SSPFRM_I2SWS_OUT
SSPCLK_I2SCLK_OUT
SSPRX_I2RXD_OUT
SSPCLK_I2SCLK_IN
SSPFRM_I2SWS_IN
SSPRX_I2SRXD_IN
SSPFSSIN
SSPCLKOUT
SSP
I
2
S CONVERTER
SSPRXD
SSPCLKIN
SSPFSSIN
SSPRXD