CC2520_11 Datasheet, PDF (53/133 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
13.4 Status Byte
All instructions sent over the SPI to CC2520 result in a status byte being output on SO when the first byte of
the instruction is clocked in on SI. The status byte is latched internally when a falling edge is detected on
CSn and on the last falling edge of SCLK within each byte. The latched status value is then shifted out on
the following falling SCLK edges.
The SNOP instruction can be used to read the status byte without causing any side effects.
Bit no
7
6
5
4
3
2
1
0
Signal
XOSC stable and running
RSSI valid
EXCEPTION channel A
EXCEPTION channel B
DPU H active
DPU L active
TX active
RX active
Table 13: Status byte contents
Status byte (MSB clocked out first)
Description
0: XOSC off or not yet stable
1: XOSC stable and running (Digital part has clock)
0: RSSI value is not valid
1: RSSI value is valid
0: No exceptions selected in EXCMASKAn has corresponding flag
in EXCFLAGn set
1: At least one exception selected in EXCMASKAn has
corresponding flag EXCFLAGn set
0: No exceptions selected in EXCMASKBn has corresponding flag
in EXCFLAGn set
1: At least one exception selected in EXCMASKBn has
corresponding flag EXCFLAGn set
0: No high priority DPU instruction is currently active.
1: A high priority DPU instruction is currently active.
0: No low priority DPU instruction is currently active.
1: A low priority DPU instruction is currently active.
0: Device is not in TX mode
1: Device is in TX mode
0: Device is not in RX mode
1: Device is in RX mode
13.5 Command Strobes
Most of the instructions in section 15.3 that are only one byte long are referred to as command strobes.
There are two exceptions to this: SNOP and SXOSCON. SNOP is used to read the status byte without
causing any side effects. SXOSCON turns on the crystal oscillator and must be run via the SPI. It is not
possible to load SXOSCON into the instruction buffer using IBUFLD and then execute it using IBUFEX.
The command strobes can be executed by configuring GPIO pins as input in accordance to GPIO
configuration table in section 12.6 and be triggered with a selected edge in the GPIOPOLARITY register.
Thus SPI traffic can be omitted for command strobes.
There are also two channels, X and Y, for binding exceptions to the command strobes, so that CC2520 may
automatically react to different internal events. This feature is described in more detail in section 16.1.
13.6 Command Strobe Buffer
The command strobe buffer provides another mechanism for execution of command strobes. The buffer is
loaded with the help of the IBUFLD instruction sent via SPI. Once the buffer is loaded, the instruction is
executed when CC2520 receives the SIBUFX strobe. The SIBUFX strobe can be triggered from any of the
triggering sources (SPI, GPIO, exceptions bound to SIBUFX instruction). When the instruction in the
instruction buffer has been executed, it is replaced by a SNOP instruction. If both the SIBUFEX strobe and
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