[Oberon] Serial UART question

Magnus Karlsson magnus at saanlima.com
Sun May 17 16:51:23 CEST 2020

The FT2232H chip from FTDI can operate in different modes.  One is as a 
UART with signals like RXD, TXD, RTS abd DTS.  Another mode is "245 
FIFO" where the interface looks like an 8-bit FIFO with signals like RD, 
WR, RXF and TXE.
See the FT2232H data sheet page 9 for different usage of the pins in 
various modes: 

On Pipistrello the FT2232H is hocked up for either UART mode of FIFO 
mode while on Pepino only UART mode is supported.

The RTS and DTS signals are typically used if you need modem control.


On 5/16/2020 9:34 PM, Skulski, Wojciech wrote:
> Magnus:
>    looking at your schematics, I can see that you routed RD, WR, RxE, TxE from the FT2232 to the FPGA. Are you actually using them all in the firmware? Are the same as Rx, Tx, RTS, CTS? I have seen serial cables with just the Tx and Rx and no RTS or CTS. I have also used the cables where RTS was looped back to CTS on board and not even connected to the CPU, which did not even provided such pins.
> Looking at the NW RISC5top.v and his original UCF I can only see TxD and RxD, but not RTS or CTS.
> I wonder if these RTS and CTS are not superfluous. Why are they needed, if needed at all?
> Thank you,
> Wojtek

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