Subject: Re: Support for 16650?
To: Geoff Wing , Geoff Wing <>
From: Jukka Marin <>
List: port-i386
Date: 09/29/2000 08:13:30
On Fri, Sep 29, 2000 at 04:30:30AM +0000, Geoff Wing wrote:

> The NS16450 has a 1 byte memory space.  (The 8250 is similar to this)
> The NS16550 has a 16 byte buffer.
> The NS16650 has a 32 byte buffer.
> The NS16750 has a 64 byte buffer.
> The NS16950 has a 128 byte buffer (and external clocking).

And then there are things like ST16C654, which has 4 ports and 64-byte
FIFOs (manufactured by Exar. for example).
> You can buy boards with multiple chips of one kind.  i.e. a board
> with 4 x 16950's.
> Regards,
> -- 
> Geoff Wing : <>
> Rxvt Stuff : <>
> Zsh Stuff  : <>

On Fri, Sep 29, 2000 at 03:50:10PM +1100, Geoff Wing wrote:

> The 16950 provides automatic handshaking (RTS/CTS) and automatic RS-485
> line control (as well as external clocking for isochronous applications).
> I don't think that NetBSD supports this but that's definitely not
> authoritative information.

The UART chips are a complete mess. ;-)  The Exar ST16C654 supports automatic
RTC/CTS handshaking, but it still has no configurable interrupt request to
tell when the transmit FIFO is empty (so the software driver could switch an
RS485 transceiver back to receiving mode).  BUT, Oxford Semiconductors makes
a pin-compatible chip OX16C954 which has this feature and a bunch of others
(like freely settable FIFO tresholds instead of the four levels provided by
most other "16450 compatible" UARTs).

ST16C654 supports baud rates up to 1.5 Mbps and needs no magic to be able
to support 50 bps ... 460.8 kbps (some serial cards seem to have "turbo
jumpers" to multiply/divide the input clock to achieve this).

Why did I type all this?  Beats me, too..