Path: utzoo!utgpu!watmath!clyde!att!pacbell!ames!lll-winken!scooter!netsys!ziggy!scotty
From: scotty@ziggy.UUCP (Scott Drysdale)
Newsgroups: comp.sys.amiga
Subject: Re: Multiple Serial Ports (Re: vt100 v2.9)
Message-ID: <149@ziggy.UUCP>
Date: 11 Jan 89 04:49:25 GMT
References: <8812150227.AA09671@postgres.Berkeley.EDU> <14049@oberon.USC.EDU> <147@ziggy.UUCP> <3256@sugar.uu.net>
Reply-To: scotty@ziggy.UUCP (Scott Drysdale)
Organization: Un*x Link,Frederick Md.
Lines: 43

In article <3256@sugar.uu.net> karl@sugar.uu.net (Karl Lehenbauer) writes:
>In article <147@ziggy.UUCP>, scotty@ziggy.UUCP (Scott Drysdale) writes:
>> first of all, anyone who develops a multiport serial board that doesn't have
>> it's own CPU on board is absolutely nuts.  using interrupts from the UARTs
>> is also grounds for the electric chair.  
>
>It's not as necessary as it used to be.  With the chip I mentioned, the NEC
>16550A, it can buffer up to sixteen bytes of input data.  That means you
>can have as many as 16 times fewer interrupts...only 60 a second for one port
...
>Plus, I still need MIDI and my stuff is already ready for it from a dumb 
>port -- the default in the machine is one, after all, and the smart board
>will probably need a precision clock and internal specific intelligence
>for MIDI -- sort of like a multiport version of the Roland MPU-401.  The
>trouble is, too, it's more expensive plus the programming model is totally
>different.

that's a good point about midi timing.  it would be relatively easy to add
a mode to the board which caused it to recognize blobs of midi stuff and
append a timestamp to them.  my current idea for the board is having 64K of
dual port RAM which looks from the amiga as one 64K block (amazing - the
minimum autoconfig size!) and looks to the 80186 as 32K of data space at
location 0 and 32K of code space at F8000.  the amiga will upload the 186
code to the board, which should help as far as getting customized drivers
into the board.  as to the timing stuff, there are at least 2 (maybe 3)
timers built into the 186, and i'll be using only one of 'em for the poll
interrupt.  that's enough left for timestamp counters.

...
>I guess the point is that I had a really favorable experience with adding
>typeahead buffer in the UART, and it's less expensive and easier -- the
>16550As are 8250 pin-compatible, by the way.

that's nice - but consider that you'll need 8 8250's to take the place of
4 SCC's - or is there a dual version of the 15660A in a 40 pin package?
also, does it have it's own baud rate generator inside?

>-- 
>-- uunet!sugar!karl  | "We've been following your progress with considerable 
>-- karl@sugar.uu.net |  interest, not to say contempt."  -- Zaphod Beeblebrox IV
>-- Usenet BBS (713) 438-5018

  --Scotty