The DS90UB662-Q1 8 GPIO pins can output data received from the forward channel when paired with a DS90UB63x CSI-2 Serializer . The remote Serializer GPIO are mapped to GPIO. Each GPIO pin can be programmed for output mode and mapped. Up to four GPIOs are supported in the forward direction on each FPD-Link III Receive port. Each forward channel GPIO (from any port) can be mapped to any GPIO output pin. The DS90UB633A-Q1 GPIO’s cannot be configured as inputs for remote communication over the forward channel to the DS90UB662-Q1.

The timing for the forward channel GPIO is dependant on the number of GPIOs assigned at the serializer. When a single GPIO input from the DS90UB63x CSI-2 Serializer is linked to a DS90UB662-Q1 deserializer GPIO output the value is sampled every forward channel transmit frame. Two linked GPIO are sampled every two forward channel frames and 3-linked or 4-linked GPIOs are sampled every 5 frames. The minimum latency for the GPIO remains consistent (approximately 225 ns), but as the information spreads over multiple frames, the jitter typically increases on the order of the sampling period (number of forward channel frames). TI recommends maintaining a 4x oversampling ratio for linked GPIO throughput. For example, when operating in 4-Gbps synchronous mode with REFCLK = 25 MHz, the maximum recommended GPIO input frequency based on the number of GPIO linked over the forward channel is shown in Table 7-8. When operating in 2.0 Gbps forward channel frequency, the maximum forward channel GPIO frequency will be half of the rate as compared to 4.0 Gbps operation.

In addition to mapping remote serializer GPI, an internally generated FrameSync (see Section 7.4.24) or other control signals may be output from any of the deserializer GPIOs for synchronization with a local processor or another deserializer.