NXP Semiconductors freescale K51 Series Reference Manual

50.4.1.5 AC97 modeIn AC97 mode, the I2S transmits a 16-bit tag slot at the start of a frame and the rest of theslots (in that frame) are all 20-bits wide. The same sequence is followed while receivingdata. Refer to the AC97 specification for details regarding transmit and receive sequencesand data formats.NoteThe Audio Codec specification released in 1997 [AC '97]defines the architecture and digital Interface, specificallydesigned for implementing audio and modem I/O functionalityin personal computers. Companion specifications include theModem Codec [MC '97], and the combined Audio/ModemCodec standard [AMC '97]. The current version of AC '97 wasproduced in 2002. The AC-97 specification defines arecommended 48-pin QFP IC package.Since the I2S has only one RxDATA pin only one codec is supported. Secondary codecsare not supported.When AC97 mode is enabled, the hardware internal overrides the following settings. Theprogrammed register values are not changed by entering AC97 mode but they no longerapply to the module's operation. Writing to the programmed register fields updates theirvalues. These updates can be seen by reading back the register fields. However, thesesettings do not take effect until AC97 mode is turned off.The register bits within the bracket are equivalent settings:• Synchronous mode is entered (CR[SYN] = 1)• Network mode is selected (CR[NET] = 1)• Tx shift direction is msb transmitted first (TCR[TSHFD] = 0)• Rx shift direction is msb received first (RCR[RSHFD] = 0)• Tx data is clocked at rising edge of the clock (TCR[TSCKP] = 0)• Rx data is latched at falling edge of the clock (RCR[RSCKP] = 0)• Tx frame sync is active high (TCR[TFSI] = 0)• Rx frame sync is active high (RCR[RFSI] = 0)• Tx frame sync length is one-word-long-frame (TCR[TFSL] = 0)• Rx frame sync length is one-word-long-frame (RCR[RFSL] = 0)Chapter 50 Integrated interchip sound (I2S)K51 Sub-Family Reference Manual, Rev. 6, Nov 2011Freescale Semiconductor, Inc. 1467