Protocol decoder:Rfm12

rfm12

Name	RFM12
Description	433, 868 and 915MHz transceiver chip
Status	supported
License	GPLv2+
Source code	decoders/rfm12
Input	spi
Output	rfm12
Probes	—
Optional probes	—

The rfm12 decoder supports the control protocol for the HopeRF RFM12 transceiver chip. RF12B is a single chip, low power, multi-channel FSK transceiver designed for use in applications requiring FCC or ETSI conformance for unlicensed use in the 433, 868 and 915 MHz bands.

Hardware

These modules comes in three different form factors, DIP package (shown on the photo) and two SMD packages: S1 with normal crystal and S2 with low-profile crystal.

Pins:

Name	Function
nINT/VDI	Interrupt input (active low)/Valid data indicator
VDD	Positive power supply
SDI	SPI data input
SCK	SPI clock input
nSEL	Chip select (active low)
SDO	SPI data output
nIRQ	Interrupt request output (active low)
FSK/DATA/nFFS	Transmit FSK data input/ Received data output (FIFO not used)/ FIFO select
DCLK/CFIL/FFIT	Clock output (no FIFO )/ external filter capacitor(analog mode)/ FIFO interrupts(active high)
CLK	Clock output for external microcontroller
nRES	Reset output (active low)
GND	Power ground

Protocol

In minimal configuration the chip uses the standard SPI protocol on pins SDI, SDO, SCK and nSEL. You can optionally connect nIRQ which will be pulled low by the transceiver to trigger interrupt request. There is also an option to transmit and receive the data without the overhead of SPI protocol using dedicated DATA and DCLK pins.

SPI communication happens in a fixed length 16-bit chunks. During each exchange the microcontroller first sends the command and then receives the response.

Decoder

The rfm12 decoder stacks on top of the SPI decoder and decodes the SPI exchanges. It shows what commands where send to the chip and decodes the responses. It also interprets the commands and shows what happened to the chip.

Resources

• RFM12 page on HopeRF site
• RFM12 datasheet
• RFM12B datasheet
• RF12 IC datasheet