USGlobalsat ET-333 User Manual
Page 6
ET-333
Specifications are subject to be changed without notice.
Page 6 of 15
Version 1.3.1
Pin Explanation
GND:
GND provides the ground for the engine boards. Be sure to connect all grounds
VBAT
(Backup Battery) This is the battery backup that powers the SRAM and RTC when main power is
removed. Typical current draw is 10uA. Without an external backup battery or Gold-capacitor, the
module/engine board will execute a cold start after every turn on. To achieve the faster start, a battery or
capacitor should be installed. To maximize battery lifetime, the battery voltage should not exceed the
supply voltage and should be between 2.5v and 3.6V. (
NOTE
: This pin must be kept “HIGH” for operation.
From Vcc connect a 470 Ohm resistor in series with a 3.2v Zener diode to Ground. Then, connect the
VBAT input to Zener’s cathode to pull the input “HIGH”.)
GPI01:
User can use this I/O pin for special functions (for example, an on/off indicator LED).
VDC
(DC power input) This is the main DC supply for a 3.3V~5.5V power module board.
PBRES
(Push button reset) This pin provides an active-low reset input to the engine board. It causes the
engine board to reset and start searching for satellites.
GP101:
User can use this I/O pin for special functions (for example, an on/off indicator LED).
SELECT:
Do not connect (do not use)
TX:
This is the main transmit channel for outputting navigation and measurement data to user’s navigation
software or user-written software.
RX:
This is the main receive channel for receiving software commands to the engine board from
SiRfdemo software or from user-written software.
SELECT:
Do not connect (Reserved)
Time Mark:
This pin provides one pulse-per-second output from the engine board that is synchronized to
GPS time.
GND:
GND provides the ground for the engine boards. Be sure to connect all grounds
Mounting
Recommended mounting methods:
a. Use industrial grade double-sided foam tape. Place it on the bottom side of the engine board.
b. A recessed cavity in your housing design with a foam pad to eliminate shifting or movement.
c. Use provided mounting holes on the GPS engine board PCB.