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Appendix F - MMH2834 Modem Commands
F.5 Configuration and Default Storage Commands
Store Configuration & S-Register Params. in Non-Volitile Memory &W
The MMH2834 can store configuration parameters and S-register values in its non-volatile read/
write Random Access Memory (RAM) memory. The &W command does this, which prevents any
reconfiguration from being lost on a power-down or Reset (ATZ) condition. &W0 (or AT&W)
causes the MMN2834 to store your customized AT command settings and S-register values in its
nonvolatile RAM. &W0 also sets the modem so that it reads your customized settings stored in
nonvolatile RAM when powered down or reset. (The &W0 command only changes the settings
stored in nonvolatile RAM that you specifically intend to alter. All other default parameters are
applicable.)
&W1 causes the MMH2834 not to store your customized settings to nonvolatile RAM so that,
after powering down or resetting the modem, it reads the factory default settings stored in ROM.
Loading Factory Defaults &F
The &F command provides a choice between customized con figuration settings in RAM and the
factory default configuration settings in ROM. The &F8 and &F9 commands define the func tion
of the &F command.
The MMH2834 is shipped from the factory with a pre-configured set of command and S-register
default settings. This set of factory defaults can be recalled by issuing the &F command. In
addition to being able to recall the factory-installed defaults, the &F command can also recall
those defaults stored under &W0. This is done using the &F9 command. If you have stored
parameters with the &W0 command and wish these settings to always be used as your defaults,
you would enter &F9&W0.To return the &F command to read factory installed defaults, enter
&F8&W0. &F8 is the factory default.
Many datacomm programs, including MultiExpress
TM
and MultiExpress for Windows
TM
, issue the
&F command automatically—the &F9 command allows the user to select their own defaults. Note
that the &F8/&F9 commands should be used with &W0.
Modem Reset Z
The Z command can be used to reset the entire command mode buffer and the result is the
same as if you had disconnected, and then reconnected power to the modem. When an ATZ
command is executed, the state of the &W command determines where the default values
originate. &W0 defaults come from RAM and &W1 defaults come from ROM.
Async/Sync Mode Switching &M
This command can be used to set the on-line mode to either synchronous or asynchronous.
AT&M0 will set the MMN2834 to Asynchronous mode, and all communications will be
Asynchronous, in both On-line and Command modes. AT&M1 causes the MMH2834 to
communicate asynchronously when in Command mode and switch to synchronous mode while
on-line. The modem defaults to &M0 (asynchronous communications) on reset or power-up.
Synchronous Transmit Clock Select &X
The &X command selects the Synchronous Transmit Clock Source in conjunction with the
MuxClock ($MUXCL) command for the composite link. External clocking is the default condition.
External clocking is when the DTE provides transmit clocking to the modem on pin 24 of the
RS232C interface. &X0 is the default setting which is internal clocking. Internal clocking is when
the modem provides transmit clock to the DTE on pin 15 of the RS232C/V.24 interface. The &X1
command selects External clocking. &X2 enables Slave Clocking. The &X2 Command causes
the MMH2834 to generate the transmit clock timing (pin 15) from the receive clock (pin 17) from
the DTE (therefore 15 and 17 are the same). In this mode (Slave Clocking), all timing is
controlled by the receive clock.