CP/M/CPM_CDROM.iso/cpm/mex/mxo-px8.doc

Text File | 1994-07-13 | 12.1 KB | 205 lines

.fo  MXO-PX8 Version 1.0        -#-     (C) Copyright 1985 by David B. Kozinn
.po 0
     This  file will serve to document the MXO-PX8 overlay for MEX  version
1.12.  This file is not intended to document MEX itself, but rather some of
the  peculiarities  inherent in using this overlay.  I'll try not  to  miss
anything.

                               Installation

     MXO-PX8  should  only be installed in version 1.12 (or higher) of  MEX
since  it  relies  on  some variables that were  added  for  that  version,
specifically the MODE byte for determining when we're in terminal mode  (so
we  don't  try  to  use XON/XOFF flow control  then)  and  it  specifically
disables  the  queued  I/O mode since this interferes with the  PX-8's  own
interrupt  driven  I/O  routines.  No special procedures  are  needed  when
installing the overlay, and you may install any dialing overlay (which will
only be used if you are using an external modem) that is ORG'd at 0B00H. If
you are using an external modem dialing overlay (see the section on Dialing
Overlays  for  details),  you must have it after the main overlay  in  your
MLOAD command or it will not be recognized.  A typical MLOAD command  might
look like this:

          MLOAD MEX.COM=MEX112.COM,MXO-PX8.HEX,MXO-SM14.HEX


                             The SET commands

     SET  ?  will  tell  you  what what the  available  SET  commands  are.
Currently these are SET, SET DELAY, SET OFFHOOK, and SET COMM.

     SET by itself will return some information about the current status of
the RS-232 ports.  The information returned is carrier status,  whether the
modem is on or off hook,  and what the DELAY value is (see below.) A couple
of caveats about this information: if you exit MEX then re-enter the on/off
hook  status will be incorrect if the modem is off-hook when you enter.  If
you have something plugged into the external RS-232 port that is  providing
DTR  then  you will always appear to have carrier no matter whether or  not
there is really carrier present to the modem.

     SET  DELAY  changes  the  delay value that is used  when  a  comma  is
encountered  in  a dialing string.  (See the section on  dialing  for  more
information.)  The default value is two seconds,  but any value from 0 to 9
may be used.

     SET  OFFHOOK causes the modem to go off-hook.  This probably  isn't  a
really useful thing in most cases,  except that if you've disconnected when
using  the  external  port,  you'll need to say this to make the  port  pay
attention to you.

     SET  COMM is the most useful of the SET commands.  When you  type  SET
COMM  you'll  get a menu that looks pretty much like the menu that you  get
from  CONFIG.  The only difference is that on the last line you can  select
either  the EXTERNAL or INTERNAL modem.  In this case EXTERNAL refers to  a
device plugged into the RS-232 plug on the back of the PX-8, which INTERNAL
refers  to an MFU or other direct connect modem connected directly  to  the
system bus.  (In other words, it's got to be attached to the bottom of your
PX-8.) The system will not let you select the internal modem if you haven't
got  one.  When you first start up the system,  the values selected are the
ones  that  you have set up to be your  default  communications  parameters
using CONFIG.  The only exception to this is whether to use the internal or
external  modem (since CONFIG doesn't handle that.) If an internal modem is
present,  it will be the default,  otherwise external will be assumed. When
you  exit MEX,  your overlay parameters will be retained as long as you  do
not do a warm boot (ie.  type control-c or do a jump to 0000H.) A warm boot
will cause the modem to power off, hanging up the phone line in the process
(if it was connected.) More about this later.

                             Dialing Overlays

     If you don't have an MFU (which I use to mean an actual multi-function
unit  or  a  system-bus connected modem) then you'll  need  to  include  an
overlay such as MXO-SM14 when you MLOAD to create your MEX.  If you do have
an  MFU,  you  may  include  such a dialing overlay  as  well  for  maximum
flexibility,  as  you'll  then be able to dial using both the internal  and
external modem.  It won't cost you anything else in terms of space since if
you  don't install the dialing overlay that space is still in the  program,
though unused.  If you choose to use an external dialing overlay,  you  may
also choose how you want the modem to disconnect from the line.  If you set
the  DISC equate to FALSE,  then the modem will disconnect by dropping DTR.
If you set it to TRUE,  then the character sequence to disconnect the modem
from the line will be used instead.  (If the preceeding few sentences don't
mean anything to you just forget about it,  MEX will do the right thing for
you.I won't discuss the use of the external modem dialing overlay any more,
as  it  is  documented  elsewhere.  The rest  of  this  section  will  deal
exclusively with the internal modem dialing routines.

     As "delivered",  the MXO-PX8 overlay supports dialing via the built in
modem  in  a DTMF (tone) mode only.  (Future revisions of this overlay  may
support  pulse  dialing.)  The modem itself is capable  of  generating  all
sixteen DTMF tones,  which includes the familiar digits (0-9), #, and *, as
well as the rarely-seen (or heard) A,B,C,  and D tones.  (If you don't know
what the A-D tones are used for,  don't worry about it, you're not the only
one.  I've  included  them since they are supported by the  hardware.)  The
comma (,) is also specially supported: A comma in the dialing string causes
the dialing routine to wait approximately DELAY seconds.  DELAY is set with
the  SET  DELAY  command as previously mentioned,  and  the  default  is  2
seconds.  You may include several commas in a row if you need to. All other
characters  are ignored.  The current version of the overlay will not allow
you to send tones on a line that is already active,  it will hang up  first
then attempt to dial the tones.

                      Automatic XON/XOFF flow control

     The  PX-8  is  a  wonderful piece of  electronics,  but  one  of  it's
drawbacks is a rather slow LCD display screen.  Because the screen is slow,
it's  easy  to overrun the internal buffer with characters coming in  while
the display is trying valiantly to keep up.  (By the way, this is generally
only  a  problem at speeds at or above about 1200 baud,  but can  occur  at
lower  speeds if you get a lot of linefeeds in rapid  succession.  This  is
because  the  screen scrolls even slower than it writes.) Because of  this,
I've chosen to implement automatic flow control while in terminal mode.

     When  the  internal buffer (which is about 360 bytes) gets  about  3/4
full,  an  X-OFF (ASCII character 11H) is sent out through the modem  port.
When  the buffer becomes nearly empty,  an X-ON (ASCII 13H) is  sent.  Many
computers  (both  mainframes and micros) alike will honor this  signal  and
will stop sending when told to.  If not, then you'll somehow have to insure
that  data is sent in small enough chunks so that the buffer does  not  get
overrun.  You  can  tell if this has happened since you'll the  data  being
displayed will not look like anything you were expecting.  (In other words,
you're going to get junk on the screen.) The overlay will only do this kind
of flow control while in terminal mode,  since it would interfere with file
transfers  using either file transfer protocol,  and because it just  plain
isn't needed then.

                            File Transfer Speed

     A  word  or  two about file transfer speed.  MEX is  a  big,  flexible
program.  The PX-8 is a small,  powerful,  but not-too-fast  computer.  The
combination of those two things does have it's price.  The price is that it
is  not  really possible to get the maximum theoretical speed at any  given
baud rate.  The higher the baud rate,  the lower the percentage of  maximum
you'll  get.  What  this  means is that you should not expect  to  get  the
transfer time that MEX tells you when you start a file transfer.  At higher
baud  rates,  you'll probably need to multiply that figure by 3-4 times  to
get the actual transfer time.  The good news is that even though you aren't
getting  the  theoretical  maximum  rate,  you can still hook  up  to  your
favorite  computer  at it's maximum speed without  worrying  about  loosing
characters during file transfer.

                         More Speed-related Stuff

     It  has  been reported that if you are using a floppy disk drive  with
your  PX-8 that you may have problems with the other end timing  out  while
you  write  (or  read) to disk.  This is most likely due to the  fact  that
normally MEX writes 128 sectors at a time to disk,  which is a fairly  slow
process with the battery powered external modem.  If you have problems, you
can  try  telling MEX to buffer smaller amounts between  disk  writes.  The
simplest  way  to  do  is by using the POKE command then  using  the  CLONE
command to produce a new working copy of MEX. The procedure is very simple.
When in MEX, simply type:
                             POKE $D23,n
Replace n with the size of the buffer that you want to use.  I recommend 4,
which  will cause MEX to save 32 sectors (ie.  4K bytes) in  memory  before
writing  to disk.  Then simply use the CLONE command to save a new copy  of
MEX.

     Since  it's impossible to tell when a user of MEX might want to return
to  terminal mode,  I've chosen to implement the overlay in a  manner  such
that the RS-232 port is always left powered on,  even when exiting to CP/M.
(This  is so that you can leave MEX then return and pick up right where you
left off.) Because of this,  there is a constant drain on the batteries. If
you intend to use your PX-8 for any length of time after using MEX  without
turning  it  off,  then be sure to do a warm boot (by typing  a  control-C)
sometime  after exiting MEX.  This will cause the RS-232 port and the modem
to power off, and will result in extended battery life.

                               Miscellaneous

     I've found it helpful to do a STAT PAGE 8 then CLONE so that the  STAT
display  doesn't  roll off my screen before I've had a chance to  read  it.
You'll  probably want to change the default <ESC> sequence from <LF>  since
there  is no LF key on the PX-8 keyboard.  (If you don't want to,  remember
that you can always type control-J to send a linefeed.) Some of the  timing
values  used for file transfer speed will be less accurate than usual since
MEX  didn't  define values for some of the baud rates.  See  the  code  for
specifics. You'll probably want to use CONFIG to set your default baud rate
to  300 if you're going to be using an MFU.  That makes it possible to  use
the mode without having to use the SET COMM menu.

                        Notes About the Source Code

     I've  tried  to make the source code as readable as possible  so  that
others  can  build upon what I've started.  I ask that if you enhance  this
overlay,  you let me know so that I can keep my own versions up to date. In
addition,  I'll  be glad to answer any questions that I can about  how  the
overlay works.

                                  Thanks

     Special  thanks  for  the  help they've given me  in  developing  this
overlay must go to Justin Bell,  Chuck Freeman, and Mike Morra of Epson for
their help in getting me the information I needed to access the PX-8 system
information,  to Ron Fowler for tolerating my questions about MEX,  to John
Kinney and Charlie Strom for helping me to beta-test the overlay, and to my
wife  Sharon  for putting up with me while I tried to get the  overlay  put
together.

          David B. Kozinn     March 5,1985

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