Datasheet

Revision 1.5 Page 16 of 41
nRF905 Product Specification
8 Modes of Operation
The nRF905 has two active (RX/TX) modes and two power saving modes:
8.1 Active Modes
• ShockBurst™ RX
• ShockBurst™ TX
8.2 Power Saving Modes
• Power down and SPI programming
• Standby and SPI programming
The nRF905 mode is decided by the settings of TRX_CE, TX_EN and PWR_UP.
Table 11. nRF905 operational modes.
8.3 nRF ShockBurst™ Mode
The nRF905 uses the ShockBurst™ feature. ShockBurst™ makes it possible to use the high data rate
offered by the nRF905 without the need of a costly, high-speed microcontroller (MCU) for data processing/
clock recovery. By placing all high speed signal processing related to RF protocol on-chip, the nRF905
offers the application microcontroller a simple SPI, the data rate is decided by the interface speed the
microcontroller sets up. By allowing the digital part of the application to run at low speed, while maximizing
the data rate on the RF link, the nRF905 ShockBurst™ mode reduces the average current consumption in
applications. In ShockBurst™
RX, Address Match (AM) and Data Ready (DR) notifies the MCU when a
valid address and payload is received respectively. In ShockBurst™ TX, the nRF905 automatically gener-
ates preamble and CRC. Data Ready (DR) notifies the MCU that the transmission is completed. This
means reduced memory demand in the MCU resulting in a low cost MCU, as well as reduced software
development time.
8.4 Typical ShockBurst™ TX
1. When the application MCU has data for a remote node, the address of the receiving node (TX-
address) and payload data (TX-payload) are clocked into nRF905 through the SPI. The applica-
tion protocol or MCU sets the speed of the interface.
2. MCU sets TRX_CE and TX_EN high, this activates a nRF905 ShockBurst™ transmission.
3. nRF905 ShockBurst™ does the following:
X Radio is automatically powered up.
X Data packet is completed (preamble added, CRC calculated).
X Data packet is transmitted (50kbps).
X Data Ready is set high when transmission is completed.
PWR_UP TRX_CE TX_EN Operating Mode
0 X X Power down and SPI programming
1 0 X Standby and SPI programming
1 X 0 Read data from RX register
1 1 0 Radio Enabled - ShockBurst™ RX
1 1 1 Radio Enabled - ShockBurst™ TX