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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
454 of 808
NXP Semiconductors
UM10360
Chapter 20: LPC17xx I2S interface
5.11 Transmit Clock Rate register (I2STXBITRATE - 0x400A 8028)
The bit rate for the I
2
S transmitter is determined by the value of the I2STXBITRATE
register. The value depends on the audio sample rate desired, and the data size and
format (stereo/mono) used. For example, a 48 kHz sample rate for 16-bit stereo data
requires a bit rate of 48,000
×
16
×
2 = 1.536 MHz.
5.12 Receive Clock Rate register (I2SRXBITRATE - 0x400A 802C)
The bit rate for the I
2
S receiver is determined by the value of the I2SBITRXRATE register.
The value depends on the audio sample rate, as well as the data size and format used.
The calculation is the same as for I2SRXBITRATE.
5.13 Transmit Mode Control register (I2STXMODE - 0x400A 8030)
The Transmit Mode Control register contains additional controls for transmit clock source,
enabling the 4-pin mode, and how MCLK is used. See
for a summary of
useful mode combinations.
Table 395: Receive Clock Rate register (I2SRXRATE - address 0x400A 8024) bit description
Bit
Symbol
Description
Reset
Value
7:0
Y_divider
I
2
S
receive
MCLK rate denominator. This value is used to divide
PCLK to produce the
receive
MCLK. Eight bits of fractional divide
supports a wide range of possibilities. A value of zero stops the
clock.
0
15:8
X_divider
I
2
S
receive
MCLK rate numerator. This value is used to multiply
PCLK by to produce the
receive
MCLK. A value of zero stops the
clock. Eight bits of fractional divide supports a wide range of
possibilities. Note: the resulting ratio X/Y is divided by 2.
0
31:16
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
Table 396: Transmit Clock Rate register (I2TXBITRATE - address 0x400A 8028) bit
description
Bit
Symbol
Description
Reset
Value
5:0
tx_bitrate
I
2
S transmit bit rate. This value plus one is used to divide
TX_MCLK to produce the transmit bit clock.
0
31:6
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
Table 397: Receive Clock Rate register (I2SRXBITRATE - address 0x400A 802C) bit
description
Bit
Symbol
Description
Reset
Value
5:0
rx_bitrate
I
2
S receive bit rate. This value plus one is used to divide
RX_MCLK to produce the receive bit clock.
0
31:6
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA