Overview
This module has a DS1307, a battery socket and three pull-up resistors on the PCB. It uses I2C protocol to communicate with external I2C master (Arduino board, PIC, AVR, etc.). The SQW/OUT pin of DS1307 is broke out via a 3-pin interlock connecter. A 4-pin connector eases the wiring to an Arduino Sensor Shield. The three pull-up resistors are connected to SDA, SCL, and SQW respectively, and they are clearly noted on the silkscreen of the PCB. User could take them off board if those pull-up resistors have already been implemented somewhere else off the module.