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1108
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
24.0.21.2.2 Time-Division Multiplexed (TDM) Transfer Mode
The McASP time-division multiplexed (TDM) transfer mode supports the TDM format discussed in
.
Transmitting data in the TDM transfer mode requires a minimum set of pins:
•
ACLKX - transmit bit clock
•
AFSX - transmit frame sync (or commonly called left/right clock)
•
One or more serial data pins, AXR[n], whose serializers have been configured to transmit
The transmitter has the option to receive the ACLKX bit clock as an input, or to generate the ACLKX bit
clock by dividing down the AHCLKX high-frequency master clock. The transmitter can either generate
AHCLKX internally or receive AHCLKX as an input. See
.
Similarly, to receive data in the TDM transfer mode requires a minimum set of pins:
•
ACLKR - receive bit clock
•
AFSR - receive frame sync (or commonly called left/right clock)
•
One or more serial data pins, AXR[n], whose serializers have been configured to receive
The receiver has the option to receive the ACLKR bit clock as an input or to generate the ACLKR bit clock
by dividing down the AHCLKR high-frequency master clock. The receiver can either generate AHCLKR
internally or receive AHCLKR as an input. See
and
.
The control registers must be configured as follows for the TDM mode. The TDM mode specific bit fields
are in bold face:
•
PFUNC: The clock, frame, data pins must be configured for McASP function.
•
PDIR: The clock, frame, data pins must be configured to the direction desired.
•
PDOUT, PDIN, PDSET, PDCLR: Not applicable. Leave at default.
•
GBLCTL: Follow the initialization sequence in
to configure this register.
•
AMUTE: Program all fields according to mute control desired.
•
DLBCTL: If loopback mode is desired, configure this register according to
, otherwise
leave this register at default.
•
DITCTL: DITEN must be left at default 0 to select TDM mode. Leave the register at default.
•
RMASK/XMASK: Mask desired bits according to
and
•
RFMT/XFMT: Program all fields according to data format desired. See
•
AFSRCTL/AFSXCTL: Set
RMOD/XMOD
bits to 2-32 for TDM mode. Configure other fields as desired.
•
ACLKRCTL/ACLKXCTL: Program all fields according to bit clock desired. See
.
•
AHCLKRCTL/AHCLKXCTL: Program all fields according to high-frequency clock desired. See
.
•
RTDM/XTDM: Program all fields according to the time slot characteristics desired.
•
RINTCTL/XINTCTL: Program all fields according to interrupts desired.
•
RCLKCHK/XCLKCHK: Program all fields according to clock checking desired.
•
SRCTLn: Program all fields according to serializer operation desired.
•
DITCSRA[n], DITCSRB[n], DITUDRA[n], DITUDRB[n]: Not applicable. Leave at default.
24.0.21.2.2.1 TDM Time Slots
TDM mode on the McASP can extend to support multiprocessor applications, with up to 32 time slots per
frame. For each of the time slots, the McASP may be configured to participate or to be inactive by
configuring XTDM and/or RTDM (this allows multiple CPUs to communicate on the same TDM serial bus).
The TDM sequencer (separate ones for transmit and receive) functions in this mode. The TDM sequencer
counts the slots beginning with the frame sync. For each slot, the TDM sequencer checks the respective
bit in either XTDM or RTDM to determine if the McASP should transmit/receive in that time slot.