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SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
24.0.21.2.3.2 Transmit DIT Clock and Frame Sync Generation
The DIT transmitter only works in the following configuration:
•
In transmit frame control register (AFSXCTL):
–
Internally-generated transmit frame sync, FSXM = 1
–
Rising-edge frame sync, FSXP = 0
–
Bit-width frame sync, FXWID = 0
–
384-slot TDM, XMOD = 1 1000 0000b
•
In transmit clock control register (ACLKXCTL), ASYNC = 1
•
In transmit bitstream format register (XFMT), XSSZ = 1111 (32-bit slot size)
All combinations of AHCLKX and ACLKX are supported.
This is a summary of the register configurations required for DIT mode. The DIT mode specific bit fields
are in bold face:
•
PFUNC: The data pins must be configured for McASP function. If AHCLKX is used, it must also be
configured for McASP function. Other pins can be configured to function as GPIO if desired.
•
PDIR: The data pins must be configured as outputs. If AHCLKX is used as an input reference, it should
be configured as input. If internal clock source AUXCLK is used as the reference clock, it may be
output on the AHCLKX pin by configuring AHCLKX as an output.
•
PDOUT, PDIN, PDSET, PDCLR: Not applicable for DIT operation. Leave at default.
•
GBLCTL: Follow the initialization sequence in
to configure this register.
•
AMUTE: Program all fields according to mute control desired.
•
DLBCTL: Not applicable. Loopback is not supported for DIT mode. Leave at default.
•
DITCTL:
DITEN
bit must be set to 1 to enable DIT mode. Configure other bits as desired.
•
RMASK: Not applicable. Leave at default.
•
RFMT: Not applicable. Leave at default.
•
AFSRCTL: Not applicable. Leave at default.
•
ACLKRCTL: Not applicable. Leave at default.
•
AHCLKRCTL: Not applicable. Leave at default.
•
RTDM: Not applicable. Leave at default.
•
RINTCTL: Not applicable. Leave at default.
•
RCLKCHK: Not applicable. Leave at default.
•
XMASK
: Mask desired bits according to the discussion in this section, depending upon left-aligned or
right-aligned internal data.
•
XFMT: XDATDLY
= 0.
XRVRS
= 0.
XPAD
= 0.
XPBIT
= default (not applicable).
XSSZ
= Fh (32-bit
slot). XBUSEL = configured as desired.
XROT
bit is configured according to the discussion in this
section, either 0 or 8-bit rotate.
•
AFSXCTL
: Configure the bits according to the discussion in this section.
•
ACLKXCTL
:
ASYNC
= 1. Program CLKXDIV bits to obtain the bit clock rate desired. Configure
CLKXP and CLKXM bits as desired, because CLKX is not actually used in the DIT protocol.
•
AHCLKXCTL
: Program all fields according to high-frequency clock desired.
•
XTDM
: Set to FFFF FFFFh for all active slots for DIT transfers.
•
XINTCTL: Program all fields according to interrupts desired.
•
XCLKCHK: Program all fields according to clock checking desired.
•
SRCTLn: Set
SRMOD
= 1 (transmitter) for the DIT pins. DISMOD field is don't care for DIT mode.
•
DITCSRA[n], DITCSRB[n]
: Program the channel status bits as desired.
•
DITUDRA[n], DITUDRB[n]
: Program the user data bits as desired.