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Re: [N8VEM: 14032] Re: 16C550C UART Auto Flow Control

Wayne,

Flow control has been a pain in my side since the SBC (Z80) v1.  Using the MAX232, this board made DTR/DSR available.  The SBC-188 was patterned on this board.  DTR/DSR is what my a/n terminal implements.

But with the N8, RTS/CTS was supported by the Z180.  Even the SBC v2 had jumpers (quite an array) to use either DTR/DSR or RTS/CTS.  This means I use special wiring of the cable to my a/n terminal.  Ugh!  I can't switch the terminal between one protocol or the other.  :'(

That is why the MF/PIC board allows stuffing with either a MAX232 (easy to obtain & cheap) or a MAX235 (harder to find, more expensive).  The MAX235 has 5 receivers and 5 transmitters, rather than 2 apiece in the MAX232.


So we have:

        SBC v1            DTR/DSR
        SBC v2            RTS/CTS or DTR/DSR
        Zeta                DTR/DSR
        N8                   RTS/CTS
        SBC-188          DTR/DSR
        Mini-68K uses MF/PIC board

        MF/PIC             DTR/DSR (MAX232 stuffing)
                                RTS/CTS and/or DTR/DSR (MAX235 stuffing)

I guess this is a problem that I just have to live with.  However, I like very much the idea of using the flow control that is implemented in the UART chip hardware.  I'll hang on to my funny conversion cable for a while.

--John

                               

On 06/25/2012 09:55 PM, Wayne Warthen wrote:
So, yet another follow-up on this UART flow control thing.  I received a few NXP 16C560B UART chips today.  These are DIP style UARTs that are fully 16C550 compatible.  I was able to confirm that these do implement automatic hardware flow control (RTS/CTS) properly.  So, the good news is that for anyone that cares about hardware flow control, this is an excellent choice -- it replaces your existing 16C550 without any trouble.

I am running a baud rate of 115,200bps with zero dropped characters and smooth file transfers!

The next release of RomWBW will allow this auto flow control to be enabled via a build option.  Your ECB board, terminal/emulator, and cables MUST properly support the RTS/CTS signals (null modem cables are generally fine).

At present N8VEM Z80 SBC V2 can be configured for RTS/CTS operation and works great with the NXP chip.

N8 uses only the built-in ASCI ports of the Z8S180, so it does not support the NXP chip.

Zeta is hardwired for DTR/DSR, so it currently does not support this style of auto flow control using the NXP chip.

Sergey, I know you don't want to make Zeta any more complicated, but perhaps it is worth considering switching from DTR/DSR to RTS/CTS (no jumpers) in a future Zeta revision (or even possibly use a MAX235 to support all lines).  I think RTS/CTS is the more common form of hardware flow control and would allow the auto flow control to work.

Thanks,

Wayne
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