SPRUIV7 User guide

SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP

12.1.1.4.3 MCASP Serializers

The MCASP serializers shift serial data in (Rx) and out (Tx) of the MCASP. A given serializer n consists of a shift register (XRSRn) with a single-entry data buffer XRBUFn used either for transmitting (write accessible in the MCASP_XBUFn register) or for receiving (read accessible in the MCASP_RBUFn register) data. In addition, each serializer has a dedicated control register (MCASP_SRCTLn) and a serial bidirectional data pin - AXRn. The register MCASP_SRCTLn allows n-th serializer to be configured as a transmitter, receiver, or as inactive. There are transmit and receive data formatting units to support data alignment options of the MCASP which are shared between all Tx and Rx serializers, respectively.

A given serializer XRSRn shifter configured as a receiver in the MCASP_SRCTLn register, shifts in data through MCASP corresponding device level bidirectional data pad AXRn. A given serializer XRSRn shifter configured as a transmitter in the MCASP_SRCTLn register, shifts out data on MCASP corresponding device level bidirectional data pad AXRn (n = 0 to 15).

The serializer is clocked from the transmit section clock (ACLKX signal) if configured to transmit or clocked from the receive section clock (ACLKR signal) if configured to receive. A serializer configured to transmit and receive operates in lockstep, which means that for MCASP there are at most a couple of zones, one for transmit and one for receive.

Figure 12-15 shows the serializer block diagram.

Figure 12-15 Individual Serializer and Connections Within MCASP

Transmission on the n-th serializer is performed as follows:

The MCASP is serviced by writing data into the MCASP_XBUFn register, which is an alias of the serializer data buffer - XRBUFn for transmit function. The data automatically passes through the transmit format unit before reaching the XRBUFn register in the serializer. The data is then copied from the XRBUFn to XRSRn and shifted out from AXRn synchronously to the serial clock.

Reception from the n-th serializer is performed as follows:

The data is shifted into the MCASP XRSRn serializer register through the AXRn pin, bit by bit. Once the entire slot becomes available within the XRSRn shift register, the data is copied into the serializer data buffer - XRBUFn, and can be accessed in the MCASP_RBUFn register, which is an alias of the serializer data buffer - XRBUFn for receive function. When software reads the data from this register, the MCASP passes the data through the receive format unit, hence it returns the formatted data.

Serializer controls:

A serializer n is configured as inactive via setting MCASP_SRCTLn[1-0] SRMOD bit field to 0x0.

For a transmitting serializer, the MCASP_SRCTLn[3-2] DISMOD bitfield, defines the AXRn pin output state, during inactive slots (HIGH, LOW or Hi-Z).

Transmit function for the n-th serializer is selected via setting MCASP_SRCTLn[1-0] SRMOD bit field to 0x1.

Receive function for the n-th serializer is selected via setting MCASP_SRCTLn[1-0] SRMOD bit field to 0x2 (n = 0 to 15).

In the DIT-transmission mode (that is S/PDIF format data transmission): in addition to the data, the serializer shifts out other DIT-specific information accordingly (preamble, user data, etc.). For more information, see Section 12.1.1.2.2.5, S/PDIF Coding Format.