41.6.5.1 Transmission of Commands in Video Mode

The DSI host supports the transmission of commands, both in high-speed and low-power, while in Video mode. Vertical and horizontal porch periods are used to transmit commands inserted through the user interface. Those periods correspond to the shaded areas of the figure below:

Figure 41-7. Command Transmission Periods within the Image Area

Commands are transmitted in the blanking periods after the following packets/states:

  • Vertical Sync Start (VSS) packets, if the video sync pulses are not enabled
  • Horizontal Sync End (HSE) packets, in the VSA, VBP, and VFP regions
  • Horizontal Sync Start (HSS) packets, if the video sync pulses are not enabled in the VSA, VBP, and VFP regions
  • Horizontal Active (HACT) state

The DSI host does not send commands in the last line unless a command does not fit into any blanking period area. In this case, it is postponed to the last line, causing the violation of the line time for Video mode.

There can be only one command sent in Low-Power mode per line. However, one Low-Power mode command is possible for each line.

In high-speed, the DSI host can send more than one command and as many as the host determines can fit in the available time.

The Color Mode and Shutdown signals controlled by the LCDC are also able to trigger the transmission of command packets. For details, refer to the section LCD Controller (LCDC). The commands are DSI data types Color Mode On, Color Mode Off, Shut Down Peripheral, and Turn On Peripheral. These commands are not sent in the VACT region. If the bit LP_CMD_EN in the Video Mode Configuration register (DSI_VID_MODE_CFG) is 1, these commands are sent in LP mode. In LP mode, the field OUTVACT_LPCMD_TIME in the Input Video Timing for Low-Power Commands Configuration register (DSI_DPI_LP_CMD_TIM) is used to determine if these commands can be transmitted. It is assumed that DSI_DPI_LP_CMD_TIM.OUTVACT_LPCMD_TIME is greater than or equal to four bytes (number of bytes in a short packet).

If DSI_VID_MODE_CFG.FRAME_BTA_ACK_EN is set to 1, a Bus Turn-Around (BTA) is generated by the DSI host after the last line of a frame. This may coincide with a write command or a read command.