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SW3-1 − Fast Poll Auto Rate/FSK
SW3-1 ON = Low-Speed Mode (FSK)
OFF = High-Speed Mode (Fast Poll)
The modem has two operating modes:
FSK mode, which supports data rates from 0 to 1800 bps.
Fast-poll mode, which supports data rates of 4800 and 9600 bps.
SW3-1, along with the Data Rate Selector (DRS) pin on the modem’s
RS-232 connector, configures the modem for either FSK or fast-poll
mode. Table 2-6 shows how SW3-1 and the DRS signal configure the
modem for these operating modes.
Table 2-6. Modem Operating Mode
To Select… Set SW3-1 to… And the DRS Signal…
Fast-poll mode OFF Is not connected or is set
HIGH
FSK mode OFF Is set LOW
FSK mode ON Doesn’t care
You should use the DRS signal in RTS control mode. It does not work
in either constant carrier mode (SW3-8 set to ON) or in the auto-RTS
mode (SW3-4 set to ON). The DRS signal is only sampled when the
transmitter is idle (when not sending a preamble, data, or a turn-off
sequence).
Note that DRS controls both the transmitter and receiver. If DRS
changes states while the modem is receiving a preamble, data, or a
turn-off sequence, the state of the receiver is unknown until the carrier
drops and a new preamble is received. We recommend that DRS does
not change states until both the local and remote modems’ transmitters
are in the idle state. When they are, both the local and remote modems’
DRS signal should change states.