I have been working with the Microchip Bluetooth Low Energy RN4020 and trying to include a microcontroller. We decided to use ATMEGA328 and communicate to the BLE through UART, which is supported by both devices. Sadly we are not succeeding. The BLE doesn’t seem to understand different ASCII commands sent by Atmega328 and when we try to read the received message on the atmega328 from the BLE, we see some unexpected ASCII responses.
After different trials, we are asking ourselves that we may need to do some logic level shifter. We may believe this because Atmega328 is a CMOS family chip (even though we are using 3.3V as VDD for it) and the RN4020 uses a UART with “3.3V TTL line” (taken from the RN4020 datasheet). We haven't found someone working with an ATMEL (AVR) chip with this Microchip BLE.
Can someone try to explain me what do they mean with a 3.3V TTL line? Are we able to connect these two devices without a logic level shifter?.