SPRUJ17H March 2022 – October 2024 AM2631 , AM2631-Q1 , AM2632 , AM2632-Q1 , AM2634 , AM2634-Q1
To reduce the CPU load when transmitting a LIN N-byte (with N = 1–8) response in interrupt mode or DMA mode, the SCI/LIN module has 8 transmit buffers, TD0–TD7 in LINTD0 and LINTD1. With these transmit buffers, an entire LIN response field can be preloaded in the TDy transmit buffers. Optionally, a DMA transfer can be done on a byte-per-byte basis when multibuffer mode is not enabled (MBUFMODE bit). Figure 13-235 illustrates the transmit buffers.
The multibuffer 3-bit counter counts the data bytes transferred from the TDy transmit buffers register if multibuffer mode is enabled, or from TD0 to SCITXSHF if multibuffer mode is disabled. The 3-bit compare register contains the number of data bytes expected to be transmitted. If the ID field is not used to convey message length (see Note: Optional Control Length Bits in Section 13.4.2.4.1.5), the LENGTH value indicates the expected length and is used instead to load the 3-bit compare register. Whether the length control field or the LENGTH value is used is selectable with the COMMMODE bit.
A transmit interrupt (TX interrupt) and a transmit ready flag (TXRDY flag), as well as a DMA request (TXDMA) can occur after transmitting a response. A DMA request can be generated for each transmitted byte or for the entire response depending on whether multibuffer mode is enabled or not (MBUFMODE bit).
The checksum byte is automatically generated by the checksum calculator and sent after the data-fields transmission is finished. The multibuffer 3-bit counter counts the data bytes transferred from the TDy buffers into the SCITXSHF register.