13.22.1 Communications Interface

A half-duplex, 9600 baud, 8-bit bidirectional communications interface is implemented on the DE2 interconnect. The interface consists of eight data bits, one Stop bit and one Start bit.

Dedicated UART hardware may be configured through PPS to transmit and receive messages over the DE2 communications interconnect.

The MOSFET Gate Driver side of the interface is an open-drain configuration and requires that the host dsPIC DSC uses an internal pull-up resistor to pull the DE2 interconnect high.

It is also recommended that the user enable open-drain (ODCx = 1) on the DE2 pin on the dsPIC side to allow for utilization of the pull-up, though it is not necessary if the line is properly configured for half-duplex communication.

The auto-baud frequency is temperature-dependent, as illustrated in Figure 13-4 . To establish proper DE2 communication, it is recommended to synchronize the host frequency by proceeding the auto-baud function alternatively, as described in Auto-Baud Function. The time from receiving the last bit of a command message to sending the first bit of the response message ranges from t_{DE2_RSP} to t_{DE2_WAIT}, corresponding to 0 µs to 3.125 ms. The host should refrain from sending additional messages until the previously requested message has been received in order to prevent overwriting the driver response message.

All DE2 interconnect pin configuration requirements are described in Communications Port (DE2 Interconnect) and provided in Auto-Baud Code Example.