Sierra Wireless DART 200 CDPD Modem - Manual (Page 108)

DART 200 CDPD Modem User’s Guide 8 Application Programming
Sierra Wireless, Inc. 8-14
Hardware flow control operation
The DART 200 communicates with the MAS using the CTS lead
(modem controlled) when receiving data, and sensing the RTS lead
(MAS controlled) when sending data.
When the modem receives data from the MAS it holds the CTS line in
the ON state and only transitions it to the OFF condition to exert flow
control (stop data transmission from the MAS).
When the modem sends data to the MAS it monitors the RTS lead from
the MAS; sending data only when RTS is ON, and stopping when the
MAS exerts flow control (wants to stop data transmission from the
modem) by transitioning RTS to the OFF condition. If Hardware Flow
Control is specified, the modem does not begin data transfer to the MAS
unless RTS is ON.
PAD operating mode
The DART 200 is capable of operating in two modes while transferring
data:
• Packet Assembler - Disassembler (PAD) mode - When in PAD mode
the internet protocol support is provided by the modem
• SLIP mode - When in SLIP mode the internet protocols are provided
by a software stack in the attached device, usually a PC
The DART uses PAD mode to provide support for UDP, TCP, and
telnet. The form of the dial command (ATDT or ATDP) specifies to the
modem whether TCP or UDP protocol should be used. However, telnet
is a TCP application; something more than the form of the dial command
is required to inform the modem that it should operate in telnet rather
than straight TCP mode. This function is provided by the \O parameter.
Telnet mode is specified by the \O1 parameter (default setting). When a
telnet session is established the modem will begin a negotiating process
with the host to determine the terminal being emulated, whether local or
remote echo will be used, as well as other operating rules for the session.
In addition, when data transfer starts only printable characters and
control characters will be passed. This mode of operation is not suitable
for any application other than telnet: it is not compatible with telemetry
requirements.
For telemetry the option should be changed to \O0 and saved with the
&W command. However, this causes some potential problems because
the \O parameter also controls the F, \M, and \T settings. Each \O setting
has a preferred setting for F, \M, and \T, which may not be compatible
with the end-user's program. The couplings are shown in Table 8-1.
CAUTION:
Whenever \O is
changed, verify that the
F, \M, and \T settings
are still appropriate for
the application.