Hello,
I am working on implementing the CR95HF RFID reader into a project, and I'm having some trouble with the external crystal starting; I'm wondering if anyone has had a similar issue.
On my design I have the CR95HF connected to an NRF52840 MCU through UART. When I send the ECHO command (0x55) over the UART bus, I do not get any response from the chip. I have verified the following:
- The chip is properly receiving 3.3V at all of its power supply pins.
- The SSI_0 and SSI_1 pins are properly tied to ground to select UART communication
- Baudrate for UART is set to 57600, the default for this chip
- I pulse the UART_RX/IRQ_IN pin low for ~150us on startup to properly select the protocol
On an oscilloscope, I can see that the XOUT pin that goes to the crystal rises to just above 0.5V on powerup, but the crystal never begins oscillation (see attached image). I am using the XRCGB27M120F3M00R0 from Murata, which is 27.12MHz with ~150 ohm ESR and 6pF load capacitance. I will provide the schematic for the entire circuit for reference.
The especially troubling part about this is that we have used this exact circuit and layout on different boards for different projects, and the CR95HF has worked just fine in those cases. It's just now on this new board that we can't get the crystal to start oscillating.
Any help would be appreciated, and if necessary I can provide more information (more scope traces, layout, etc.)
Thank you!
