Motorola M12 Oncore User's Guide download pdf (Page 52)

Chapter 3 - Receiver Descriptions

Time to First Fix (TTFF)

TTFF is a function of position uncertainty, time uncertainty, almanac age, and ephemeris age as

shown in the table below. The information shown below in Table 3.8 assumes that the antenna

has full view of the sky when turned on.

Table 3.8: Typical M12+ TTFF Information

Initial Error Age

Power-up

State

POS TIME ALMANAC EPHEMERIS

TTFF

M12+

TTFF

M12+

Timing

Hot

100

3 min 1 month < 4 hrs < 15s < 25s

Warm

100

3 min 1 month Unavailable < 40s < 50s

Cold

(default)

N/A N/A Unavailable Unavailable < 60s < 200s

N/A - Not applicable. Knowledge of this parameter has no effect on TTFF in this configuration.

First Time On

When the M12+ receiver powers up for the first time after factory shipment, the initial date and

time will be incorrect. This will force the receiver into a cold power-up state (cold start), and it will

begin to search the sky for all available satellites. After one satellite has been acquired, the date

and time will automatically be set using data downloaded from the satellite. When three or more

satellites are tracked, automatic position computation is initiated. At power down, the M12+

receiver does not remember its current configuration unless the receiver is fitted with an onboard

lithium cell or external back-up power is applied.

Initialization

When powered up, the M12+ acquisition and tracking algorithms will automatically start acquiring

satellites and will compute position when it acquires at least three. For each of the user controlled

outputs, the receiver (if battery backed) remembers the previously requested message formats

(continuous or polled) and the update rate. If no messages were active the last time the receiver

was used, it waits for an input command before it outputs any other data, even though it may

have acquired satellites and is computing position fixes internally.

The M12+ does not need to be initialized to its approximate position to acquire satellites and

compute position, nor does it require a current satellite almanac. However, the TTFF will be

considerably shorter if you help the receiver locate satellites by providing it with the current date

and approximate time, approximate local position and a current satellite almanac. This will allow

the receiver to perform a "Warm Start" vs. a "Cold Start".

Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05

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Motorola M12 Oncore User's Guide Page 52

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