Date   : Sun, 26 Jul 1987 1747:00
From   : w_smith%wookie.DEC@decwrl.dec.com (Willie Smith, LTN Components Eng.)
Subject: Macrotech ADIT board

I'd really like to hear from other users of the Macrotech ADIT
board as to how they like it and if they have found any of the
following 'gotcha's:
 
1)     While you can set the baud rates all the way up to 38.4K,
       the maximum output rate (in chars/sec) is around 1200 CPS.
       The input won't overrun at 19.2K, but the input rate seems
       to be limited to around 1800 CPS.
 
2)     Using the board in interrupt mode takes about 75 percent
       _longer_ than polling it continuously.  Any interrupt
       latency would be added to this number.
 
3)     When the board is set up for 'input' flow control (such that
       it will send XOFF when it wants the terminal to stop sending)
       the automatic chaining of input buffers is disabled and you
       are stuck with a 28 byte input buffer.
 
4)     The M-channel and V-channel are _slow_slow_slow_.  I rewrote
       my hard disk cache and RAM disk software to take advantage
       of these powerful new features and my machine ran half as fast
       as it did before.
 
5)     (I haven't tried this yet, but it's in the manual).  When you
       send XOFF (assuming 'output' flow control is enabled) the board
       will stop transmitting.  When you send _anything_else_ it will
       resume transmission.  This means you can't have the output
       stopped and still have input typeahead.
 
It's been somewhat discouraging to pay $1100+ (discount) for a
board with 16 I/O ports, onboard intelligence, and lots of neat
features only to have it produce a negative impact on the speed
of my system.  Yes my system does several things that it couldn't
do before, but the most frequent things (program source editing)
I do are noticably slower.
 
I am working with the manufacturer to try to resolve some of
these difficulties, and I'll post the results, but it's almost
to the point where I'm seriously considering building my own
custom EPROM to replace the onboard firmware.
 
Anyway, if anyone is using one of these boards, I'd really like
to hear some discussion of the pros and cons of it, and any other
misfeatures I may have missed.
 
Willie Smith
w_smith@wookie.dec.com
w_smith&wookie.dec.com@decwrl.dec.com
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