SETTING UP THE MULTITECH 224E FOR HARDWARE FLOW CONTROL
     
     
     With the  advent of modems using hardware based error correction (such
     as the  Microcom Networking  Protocol,  MNP),  several  file  transfer
     protocols making  exclusive use of this have emerged; i.e., IModem and
     YModemG.   These protocols  depend  on  the  modems  to  handle  error
     correction, and  depend on  CTS/RTS flow  control between the computer
     and modem  to ensure  that no  data overruns  occur.  In addition, the
     popular Zmodem protocol can make use of CTS/RTS flow control as well.
     
     The MultiTech  224E is  one of  the most popular 2400 baud modems that
     incorporates MNP  error correction  into its  circuitry.   Setting the
     various hardware  and software  parameters to  enable MNP  and CTS/RTS
     flow control  is somewhat  tricky, and  this document  is intended  to
     simplify that  task.   This is  geared to the MT224EH models that have
     Class 5  MNP.   For those  older models  that incorporate  Class 3 MNP
     only, some  of the  software switch  settings  will  generate  errors.
     These will not affect modem operation.  (MultiTech does have a program
     to upgrade Class 3 MNP to Class 5 MNP; contact them for information.)
     
     The MT224E  has two banks of DIP switches and three jumpers.  One bank
     of eight  switches is accessible via the rear panel of the modem.  The
     other bank  of four  switches is accessible only by removing the cover
     of the  modem.   The jumpers  are also accessible only by removing the
     cover (refer  to your  owner's manual  for instructions on opening the
     modem and  locating the switches and jumpers).  The following settings
     will enable  MNP error  correction (providing the modem that is called
     is so  equipped) and  CTS/RTS flow control.  They will also enable the
     full verbose response set of the MT224 which will keep you apprised of
     what the modem is doing, and will wait for dialtone before dialing.
     
     The setting  of the  bank of  eight switches  should be as follows (up
     refers to  the  OPEN  position):  1-UP  (DTR  normal),  2-UP  (verbose
     responses), 3-DOWN  (enable command  response), 4-UP  (enable  command
     echo), 5-UP  (enable autoanswer), 6-UP (CD & DSR normal), 7-UP (single
     line RJ11),  and 8-DOWN  (enable command  mode).  All of these are the
     factory default  settings with  the exception  of switch  1, which  is
     reversed.
     
     The setting  of the  bank of  four switches  should be  as follows (up
     refers to  the OPEN  position): 1-DOWN  (CTS  normal),  2-UP  (Dial-up
     operation), 3-UP  (wait for  dialtone), and 4-DOWN (asynch operation).
     Switches 2 and 4 are factory default, switches 1 and 3 are reversed.
     
     The jumpers  should be set as follows: RTS normal (not forced), CTS to
     follow RTS, and DSR to follow CD.
     
     The following  software switches  should be  set (use ATL5 and ATL7 to
     determine your current settings):
     
     &A0 - Answer back off             $F1 - Fall back on CR during link
     $A1 - Buffer data during link     &G0 - Guard tone off
     B1 - Wait for dialtone            &I1 - 10 min inactivity timer
     &B0 - Normal transmit buffer      $MB2400 - Set baud rate 2400
     &BS1 - Max block of 256 bytes     Q0 - Result codes on
     $BA1 - Baud adjust on             &Q0 - Multimodem responses
     &C1 - Carrier detect normal       &R1 - CTS forced on


     $D0 - DTR dialing off             $R0 - Disconnect after 12 tries
     E1 - Echo on                      &S1 - DSR normal
     &E1 - Auto reliable mode          $SB2400 - Set port speed 2400
     &E4 - CTS flow control            &T5 - Remote loop off
     &E7 - XON/XOFF pass thru on       V1 - Word responses
     &E8 - ENQ/ACK off                 &V1 - CCIT V.22 answer tone    
     &E10 - Modem flow control off     &W0 - Store parameters
     &E12 - Pacing off                 X1 - Extended result codes
     &E15 - Compression on             
     
     After you  have issued  the appropriate  commands, issue AT&W0 to save
     these settings.
     
     A few  words of  explanation on  some of the software switch settings:
     &E1 enables  automatic MNP  error correction  if  the  modem  you  are
     calling also  has MNP  enabled.  &E4 enables the CTS flow control that
     the new  file transfer protocols use to control data flow between your
     computer and the modem.  &E15 enables Class 5 if possible.  &R1 forces
     CTS initially  high so  that your communications program will know CTS
     is enabled.   The  setting of the jumpers and hardware switches ensure
     that even with &R1, flow control will work.
     
     For those  with Class  5 MNP,  there are a few alternate settings that
     will enhance throughput during file transfers.  Follow these steps:
     
     1)   Set your  communications program  for 9600 baud.  Do not allow it
          to reset the serial port speed.
     2)   Set the following software switches for the modem:
          a)     $BA0 - Turn on speed conversion (turn off baud adjust)
          b)     $SB9600 - Lock the serial port at 9600 baud
          c)     &W0 - Lock these settings into the modem
     
     I hope  that this  document helps  you if you have been having trouble
     setting up  your  MultiTech  224E  for  reliable  connects  with  flow
     control.   These settings  have been tested using Qmodem SST 3.1a with
     both the  IModem and YModemG protocols with artifically injected noise
     on the  phone line,  and we  have been  unable to  produce a  bad file
     transfer.   With a  Class 5  connection (CONNECT RELIABLE COMPRESSED),
     using the  alternate settings given above, we have achieved throughput
     of over  650 cps on an uncompressed document file, and over 290 cps on
     an ARC file, a better than 20% improvement over normal 2400 baud Class
     3 connections.
     
     S. David Klein
     The Software Society PCBoard
     201-729-7410
     11/15/87