Specifications

XT55 Hardware Interface Description

Confidential / Preliminary

mo b i l e

XT55_hd_v00.02 Page 74 of 116 17.03.2004

4.6 Serial interfaces of the XT55 GPS part

The GPS part of the XT55 module offers two serial interfaces:

SD1

· 2-wire serial interface

· Includes the SDI1 (receive) and SDO1 (transmit) lines

· Supported baud rate: 4800 bps. See also [2] for details on the used GPS protocol.

SD2

· 2-wire serial interface

· Includes the SDI2 (receive) and SDO2 (transmit) lines. It is intended for communication

with the GSM/ GPRS part of the XT55 module. See Figure 1 for details.

· Supported baud rate: 9600 bps. See also [2] for details on the used GPS protocol.

SD1 and SD2

· Both interfaces are configured for 8 data bits, no parity and 1 stop bit

· For more detailed characteristics see [2]

4.7 GPS control signals

GPS_M-RST: This pin provides an active-low reset input to the board. It causes the board

to reset and start searching for satellites. Reset is an optional input and, if

not utilized, it may be left open.

GPS_GPIO9 (T-MARK):

This pin provides 1 pulse per second output from the board, which is

synchronized to within 1 microsecond of GPS time. The output is a CMOS

level signal.

GPS_BOOTSEL:

Set this Pin to high for reprogramming the flash of the XT55 GPS part (for

instance updating to a new firmware for the XT55 GPS part).

GPS_RFPC0, GPS_RFPC1

These pins are input pins for Trickle-Power Mode control. They must be

connected externally to GPS_GPIO8 and GPS_GPIO4.

GPS_GPIO8, GPS_GPIO4:

These pins are control outputs for the Trickle-Power Mode. GPS_GPIO8

must be connected to GPS_RFPC0 and GPS_GPIO4 to GPS_RFPC1.

GPS_GPIO8, GPS_GPIO4 can also be used to control a LED. A possible

circuit is shown in Figure 24. If the LED lights permanently the GPS receiver

is searching for satellites. Is the GPS receiver in Trickle-Power Mode, the

LED flashes in rhythm, i.e. the GPS receiver receives valid positions data.

Timing differs between GPS_GPIO4 and GPS_GPIO8.

Note: By switched off Trickle power the LED will flash permanently. The reception of

satellites data can be checked by using the T-Mark, however, cannot be evaluated.