7.4.3 CSI-2 Interface

The DS90UB940N-Q1 (in default mode) takes RGB 24-bpp data bits defined in the serializer and directly maps the bits to the pixel color space in the data frame. The DS90UB940N-Q1 follows the general frame format as described per the CSI-2 standard (Figure 31). At the end of the vertical sync pulse (VS), the DS90UB940N-Q1 generates the frame end and frame start synchronization packets within the vertical blanking period. The timing of the frame start will not reflect the timing of the VS signal.

On the rising edge of the DE signal, each active line outputs as a long data packet with the defined data format (Figure 13). At the end of each packet, the data lanes Dn± return to the LP-11 state and the clock lane CLK± continues to output the high-speed clock.

The DS90UB940N-Q1 CSI-2 transmitter consists of a high-speed clock (CLK±) and data (Dn±) outputs based on a source synchronous interface. The half rate clock at CLK± is derived from the pixel clock sourced by the clock/data recovery circuit of the DS90UB940N-Q1. The CSI-2 clock frequency is 3.5 times (four MIPI lanes) or seven times (two MIPI lanes) more than the recovered pixel clock frequency. The MIPI DPHY outputs either two or four high-speed data lanes (Dn±) according to the CSI-2 protocol. The data rate of each lane is seven times (four MIPI lanes) or 14 times (two MIPI lanes) higher than the pixel clock. For example, in a 4-MPIP-line configuration at a pixel clock of 150 MHz, the CLK± runs at 525 MHz and each data lane runs at 1050 Mbps.

The half-rate clock maintains a quadrature phase relationship to the data signals and allows the receiver to sample data at the rising and falling edges of the clock (DDR). Figure 10 shows the timing relationship of the clock and data lines. The DS90UB940N-Q1 supports a continuous high-speed clock. High-speed data is sent out at data lanes Dn± in bursts. In between data bursts, the data lanes return to low power (LP) states according to the protocol defined in the D-PHY standard. The rising edge of the differential clock (CSI_CLK+ – CSI_CLK–) is sent during the first payload bit of a transmission burst in the data lanes.

Figure 31. CSI-2 General Frame Format