User Manual

7
8111A–AVR–05/08
AT86RF231
1.3 Digital Pins
The AT86RF231 provides a digital microcontroller interface. The interface comprises a slave
SPI (/SEL, SCLK, MOSI and MISO) and additional control signals (CLKM, IRQ, SLP_TR, /RST
and DIG2). The microcontroller interface is described in detail in Section 6. “Microcontroller
Interface” on page 16.
Additional digital output signals DIG1...DIG4 are provided to control external blocks, i.e. for
Antenna Diversity RF switch control or as an RX/TX Indicator, see Section 11.4 “Antenna Diver-
sity” on page 142 and Section 11.5 “RX/TX Indicator” on page 147. After reset, these pins are
pulled-down to digital ground (DIG1/DIG2) or analog ground (DIG3/DIG4).
1.3.1 Driver Strength Settings
The driver strength of all digital output pins (MISO, IRQ, DIG1, DIG2, DIG3, DIG4) and CLKM
pin can be configured using register 0x03 (TRX_CTRL_0), see Table 1-3 on page 7.
The capacitive load should be as small as possible as, not larger than 50 pF when using the
2 mA minimum driver strength setting. Generally, the output driver strength should be adjusted
to the lowest possible value in order to keep the current consumption and the emission of digital
signal harmonics low.
1.3.2 Pull-Up and Pull-Down Configuration
Pulling resistors are internally connected to all digital input pins in radio transceiver state P_ON,
see Section 7.1.2.1 “P_ON - Power-On after VDD” on page 34. Table 1-4 on page 7 summarizes
the pull-up and pull-down configuration.
In all other states, there are no pull-up or pull-down resistors connected to any of the digital input
pins. In RESET state, the pull-up or pull-down resistors are not enabled.
Table 1-3. Digital Output Driver Configuration
Pins Default Driver Strength Recommendation/Comment
MISO, IRQ, DIG1,....., DIG4 2 mA Adjustable to 2 mA, 4 mA, 6 mA and 8 mA
CLKM 4 mA Adjustable to 2 mA, 4 mA, 6 mA and 8 mA
Table 1-4. Pull-Up / Pull-Down Configuration of Digital Input Pins in P_ON State
Pins H pull-up, L pull-down
/RST H
/SEL H
SCLK L
MOSI L
SLP_TR L
=
ˆ
=
ˆ