SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The TDM format is used to transfer data between the host CPU and one or more analog-to-digital converter (ADC), digital-to-analog converter (DAC), or S/PDIF receiver (DIR) devices. An example for a 6-slot (channel) TDM transmission on one McASP data pin - AXRn is illustrated on Figure 24-113.
The TDM format uses three signals In a basic synchronous serial interface: data (AXRn), clock (CLK) and frame sync (FS). The data signal present on AXRn pin is fully synchronous to the serial clock (ACLKX or ACLKR). The data bits are grouped into words and slots (see also Section 24.6.2.2.2), the latter being also refered to as the "time-slots" or "channels" in TDM terminology. A frame consists of multiple time-slots. Each TDM frame is marked by the frame sync signal (AFSX or AFSR). The TDM transfer is continuous and periodic, with no delays between slots.
Within a certain frame, the last bit of slot N is followed immediately on the next serial clock with the first bit of the next slot N+1. On the boundary between two adjacent TDM-frames, the last bit of the last slot from the frame M, is followed immediately on the next clock cycle with the first bit of the first slot from the next frame M+1. For McASP, there is an option to offset the first bit of the first slot with a 0-,1- or 2-cycle delay from the frame sync signal.
The frame sync - AFSX/AFSR only marks the beginning of slot 0 and start of a new frame. Since it does not determine the boundaries of a slot, there is a requirement for a connected transmitter and receiver to agree on the number of transferred bits per slot.
In a typical audio system involving McASP module, a single TDM data frame is transferred during each sample period Ts of a data converter. The user has following choices to implement multiple channels: