Added support for 128 Kbps CLEAR synchronous communication (!Z=11 &M1 &J1)

Using 128 Kbps CLEAR Synchronous

The Terminal Adapter supports 128 Kbps synchronous connections with other devices that also 
support 128 Kbps synchronous connections. The way in which the channel bonding is performed
is by alternating every 8 bits between the B-channels. For instance, the data transmitted to
the host through the serial port is 8 bits from B1, 8 bits from B2, 8 bits from B1, 
8 bits from B2, etc. The data transmitted to the remote device through the B-channels is also
interleaved in the same manner (8 bits to B1, 8 bits to B2, 8 bits to B1, 8 bits to B2, etc.). 
This method is not compatible with the BONDING specification nor H.221.

To establish a 128 Kbps CLEAR synchronous call, 

- first set the TA for CLEAR mode (!Z=11)
- set the synchronous mode (&M1)
- as an option on the originating side you may set the channel bundling parameter (&J1) 
  otherwise you must enter two numbers in the dial string separated by &, !, or + 
  (see the description for &Jn).

The same type of setup should be done on the answering TA as well. If it is a MultiTech TA such
as the MTA128ST, MTA128NT, or MT128SMI, then the same commands should be given but the &J1 MUST
be set since this will let the answering TA know that it should expect a 128 Kbps CLEAR 
synchronous connection. When both sides are configured appropriately, then you may dial to
establish the connection or use DTR dialing. No CONNECT message will be given to indicate that
the connection is established. A 128 Kbps clock will appear on TCLK and RCLK whenthe connection
is ready for data transfer. Clocking will not happen until 5 seconds (or whatever S26 is set for)
after the second channel is established.

If the second channel of the connection cannot be established (such as a busy or no response or
no answer), then the originating TA will drop back to a single-channel 64 Kbps synchronous
connection. If the remote device is a MultiTech TA, then the remote TA will also drop back to a
single-channel 64 Kbps synchronous connection as long as the second call is received by the
remote TA before it rejects the call (possibly due to the second B-channel being in use by that
TA). If the answer side doesn't receive the second call but is expecting the second call (&J1 is
set), then the TA will not finish establishing the call and will drop the whole connection. If 
the originating TA's second call doesn't reach the remote TA (no answer or no response), then 
the whole connection will be torn down.


Modified &Jn to be inclusive of the CLEAR synchronous protocol.
   Command:     &Jn
   Function:    Channel Bundling (for models supporting two B-channels)
   Unit:        Decimal ASCII code
   Values:      n=0 (disable),
                n=1 (enable)
   Default:     &J0
   Description: The channel bundling option is used by the ML-PPP, SoftBonding, and CLEAR 
   synchronous protocols to determine whether a second channel should be added to the data 
   connection. Channel bundling may also be referred to as channel bonding and in essence it can
   yield a 128 Kbps data connection as opposed to a single-channel 64 Kbps data connection. &J1
   has the same affect as using the &, !, or + characters in the dial string when separating two
   numbers (e.g. ATD384020&384030<CR>). Channel bundling is affected by the use of Dynamic
   Bandwidth Allocation (DBA) (for ML-PPP and SoftBonding protocols only) which is controlled by
   S-registers S59, S60, S61, S62, and S63.