C 8 0 5 1 F 9 6 x / S i 1 0 2 x
Rev. 0.2
15
5.6. Pin Power Supply Select Switches
The C8051F960/Si1020 MCU has two VIO pins: VIO and VIORF. These VIO pins set the logic level and drive
voltage for the MCU port pins. The VIORF pin sets the level for the port pins normally supporting radio functionality:
P1.5 through P2.3. The Si1020 P2.0-2.3 pins are connected internally to the EZRadioPRO. The VIO pin sets the
level for all other port pins.
5.6.1. VIORF Select Switch (SW12)
When using the dc-dc buck converter to power the radio, set the VIORF selector switch to the VDC position. This
connects the output of the buck converter to the VIORF pin. When using the Si1020, this switch also selects the
power source for the radio. In this position, firmware controls the voltage on the VDC pin. The C8051F960/Si1020
buck converter also has a bypass switch that can power the radio from the full supply voltage. The dc-dc buck
converter and bypass switch are off by default after an MCU reset, so the VDC pin voltage is floating until firmware
turns on the bypass switch or configures the dc-dc converter.
When the VIORF selector switch is set to the VBAT position, the VIORF pin connects via hardware to the VBAT
pin. In this position, the dc-dc buck converter cannot power the radio.
The VBAT position powers the VIORF pin without any firmware. This position is more convenient for simple code
examples. Use this position for the code examples provided unless otherwise indicated.
5.6.2. VIO Select Switch (SW7)
The VIO selector switch provides the same functionality as the VIORF switch for the main VIO pin. Normally this
switch should be in the VBAT position, which will set the drive and input levels of the pins to VBAT.
Setting the switch to the VDC position connects the VIO pin to the output of the buck converter. In this position, the
battery powers the MCU, and all of the I/O ports operate at a lower voltage set by the buck converter. This option is
best if most of the I/O pins connect to a low voltage radio or other low-voltage peripherals. Most applications should
use the VBAT position.
The C2 connection requires a VIO power source and VDC is not powered by default, so the VBAT position must be
used for initial development.
5.7. UART VCP Connection Options
The MCU card features a USB virtual COM port (VCP) UART connection via the mini-B USB connector (J17). The
VCP connection uses the CP2102 USB-to-UART bridge chip.
The UART pins on the target MCU either connect to the CP2102 USB-to-UART bridge chip or to the UDP
motherboard. The MCU card has level translators with enables that normally route the UART connections to the
on-board USB-to-UART bridge chip. However, the UDP motherboard can drive the enable pins to route the UART
connections to the UDP motherboard instead of the on-board USB-to-UART bridge chip. There are two enable
signals: one with a default pull-down (UART_VCP_EN) and one with a default pull-up (UART_SYS_EN).
When using the UART with either the on-board USB-to-UART bridge or the UDP motherboard, install shorting
blocks on header P12 to connect P0.4 to MCU_TX and P0.5 to MCU_RX.
If desired, install shorting blocks for hardware handshaking on P0.6 and P0.7 on the P12 header. Hardware
handshaking is not required for most applications. Firmware must implement hardware handshaking on the target
MCU using P0.6 and P0.7. These pins also connect to the 40-pin radio card I2C signals by default. If necessary,
disconnect these signals by cutting the traces on R9 and R10.
The MCU card includes provisions to facilitate ultra-low power measurements. The UART pins of the target MCU
are completely disconnected from the USB-to-UART bridge by removing all the shorting blocks on P12. The VIO
supply powers the level translator. To remove the level-shifter current from the ultra-low power measurement, cut
the trace on the bottom of the board between the two pins of header J20. This will completely disconnect the level
translators from VIO. After cutting this trace, a shorting block is required on J20 to use the USB-to-UART bridge or
UDP UART connection.
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