37.2.10 Private Transaction

Once the Dynamic Address is assigned and the Target is operating in I3C SDR Mode (OPMD = 0b01), the Controller can communicate to the Target directly by specifying the Target’s Dynamic Address. The Controller uses a Private Write Transfer to write data to the Target directly and a Private Read Transfer to read data from the Target directly.

To address the Target directly, the Controller sends a Start or a Restart⁽¹⁾, followed by the 9-bit I3C Address Header. The address header consists of the Target’s Dynamic Address, followed by a R/W bit and an ACK/NACK bit. The R/W bit is ‘0’ (write) for Private Write Transfer and ‘1’ (read) for Private Read Transfer. The RNW status bits are set according to the R/W bit in the address header if the Target ACKs the request.⁽²⁾

If the Dynamic Address in the address header matches with the Target’s Dynamic Address in the I3CxDADR register, the Dynamic Address Match DADRIF flag is set. The ACK/NACK response from the Target depends upon the type of the transaction and the internal settings, as described in the following sections.

When a Private Transaction is initiated, the ACK/NACK response from the Target is controlled by the ACKP bit. When the ACKP bit is cleared (ACKP = 0), the Target normally ACKs a Private Write/Read request, and when the ACKP bit is set (ACKP = 1), the Target always NACKs a Private Write/Read request. For a Private Write request, this ACK/NACK response is strictly based on the ACKP bit setting and is completely independent of the status of the Receive Buffer/FIFO. However, for a Private Read request, in addition to the ACKP bit, the ACK/NACK response from the Target is also controlled by the hardware based on the status of the Transmit Buffer/FIFO. A Private Read request when the Transmit FIFO is empty (TXFNE = 0) will always result in a NACK by the Target and the Transmit Underrun TXUIF error flag is set. A Private Read request is ACK’d by the Target only when there is data available in the Transmit FIFO (TXFNE = 1) and ACKP is cleared. Refer to Table 37-6 for more information.

As a special feature, a one-shot ACK of a Private Write/Read request can be performed by setting the ACKPOS bit. This feature is intended to be used in conjunction with ACKP = 1 setting. When ACKP = 1, the Target always NACKs a Private Write/Read request. In this mode, setting the ACKPOS bit will override the auto-NACK setting and ACK the Private Write/Read request just one time, after which the ACKPOS bit is auto-cleared by the hardware.