SLDS204B October 2014 – June 2020 PGA300
PRODUCTION DATA.
The read operation requires two consecutive OWI frames to move data from the slave to the master. The first frame is the read-initialization frame. This frame tells the slave to retrieve data from a particular register location within the slave device and prepare to send the data over the OWI. The command field of the read-initialization frame specifies which control and status register page to read from. The first data field specifies which address within that control and status register page to read from. Sending data fields two to eight is optional. The slave ignores those additional data fields. The data are not sent until the master commands the data to be sent in the subsequent frame called the read-response frame. During the read-response frame, the data direction changes from master → slave to slave → master immediately after the read-response command field is sent. Enough time elapses between the command field and data field to allow the signal drivers to change direction. This wait time is 20 µs, and the timer for this wait time is located on the slave device. After this wait time is complete, the slave transmits the requested data. The master device is expected to have switched its signal drivers and to be ready to receive data. Figure 20 and Figure 21 show the two read frames that are required to complete a read operation.