
118
8111C–MCU Wireless–09/09
AT86RF231
Note:
shadowed. Although the clock setting of CLKM remains after reset, a read access to register bits
CLKM_CTRL delivers the reset value 1. For that reason it is recommended to write the previous
configuration (before reset) to register bits CLKM_CTRL (after reset) to align the radio transceiver
behavior and register configuration. Otherwise the CLKM clock rate is set back to the reset value (1
MHz) after the next SLEEP cycle.
For example, if the CLKM clock rate is configured to 16 MHz the CLKM clock rate remains at 16 MHz
after a reset, however the register bits CLKM_CTRL are set back to 1. Since CLKM_SHA_SEL reset
value is 1, the CLKM clock rate changes to 1 MHz after the next SLEEP cycle if the CLKM_CTRL
setting is not updated after reset.
9.6.5
Register Description
Register 0x03 (TRX_CTRL_0):
The TRX_CTRL_0 register controls the drive current of the digital output pads and the CLKM
clock rate. It is recommended to use the lowest value for the drive current to reduce the current
consumption and the emission of signal harmonics.
Bit [7:6] - PAD_IO
Bit [5:6] - PAD_IO_CLKM
These register bits set the output driver current of pin CLKM. It is recommended to reduce the
current capability to PAD_IO_CLKM = 0 (2 mA) if possible. This reduces power consumption
and spurious emissions.
Bit 3 - CLKM_SHA_SEL
Register bit CLKM_SHA_SEL defines if a new clock rate, defined by CLKM_CTRL, is set imme-
diately or after the next SLEEP cycle.
Bit
76
5
4
3
2
1
0
+0x03
PAD_IO
PAD_IO_CLKM
CLKM_SHA_SEL
CLKM_CTRL
TRX_CTRL_0
Read/Write
R/W
Initial Value
0
1
0
1
Table 9-12.
CLKM Driver Strength
Register Bit
Value
Description
PAD_IO_CLKM
0
2 mA
1
4 mA
26 mA
38 mA
Table 9-13.
CLKM Clock Rate Update Scheme
Register Bit
Value
Description
CLKM_SHA_SEL
0
CLKM clock rate change appears immediately
1
CLKM clock rate change appears after SLEEP cycle