Electronic – Interfacing DS1302 – is the schematic I found correct

gpiomicrocontrollerrtc

On the following website there is a project of a 7-segment clock, which uses DS1302 as RTC. The DS1302 is connected to the microcontroller in the way that I don't really understand. Can someone please answer a few questions?

  • Why has the author of the schematic added capacitors C5 and C4? AFAIK there is no need for additional capacitors, if crystal has specified load capacitance of 6pF. Is it because they've used a crystal with different load capacitance?

  • Why has the author of the schematic added pull-up resistors R13, R14, R15? AFAIK, they're also not needed. Are they driving those lines in open drain manner? If yes, why?

Please find the interfacing schematic:

partial schematic showing DS1302

partial schematic showing microcontroller pins connected to DS1302

Best Answer

Hobbyists don't always get the details correct, if it works they are happy. Follow the vendor recommendations.

The pull-ups are not only not needed, they can potentially cause harm since the DS1302 has internal pull-downs. I would guess that the author was accustomed to seeing pull-ups for I2C interfaces and thought that this was similar. The DS1302 doesn't use I2C or SPI, it is a custom interface.