C8051F850-DK-UG Datasheet, PDF (11/36 Pages) Silicon Laboratories – UDP C8051F850 MCU CARD USER’S GUIDE FOR C8051F85X/86X MCUS

C8051F850-DK-UG
5.5. VDD Power Select Switch (SW1)
The VDD power supply has two power options: UDP motherboard (PWR_VDD_OUT) and on-board +3.3 V
regulator power. The VDD Power Select switch is used to select between the two options. The +3.3 V regulator
power option is the upper +3.3_VREG position and allows the board to be powered from a diode-OR of four power
sources: 9 V Power Adapter (J6), the USB connector labeled COM PORT (J5), the USB Debug Adapter (J23), or
from the UDP motherboard bulk supply (PWR_5.0V_BULK).
5.6. Power LED (DS9)
The blue power LED provides visual feedback when the board is powered through USB, the 9 V power adapter, the
USB Debug Adapter, or from the UDP motherboard. The power LED indicates that power is available on the board
and the VDD Power Select switch must be configured properly to power the MCU.
5.7. Imeasure Jumper (JP2)
The Imeasure jumper (JP2) allows for easy access to measure the VDD current of the MCU. The shorting block for
this header is populated by default, and the direction of current is shown with a silk screen arrow. To measure the
supply current, remove the corresponding shorting block and connect a current measurement device across the
unpopulated header.
The voltage supply prior to the Imeasure jumper is the VDD pre-measure (VDD_PM) net, which supplies all of the
external LEDs, switches, USB COM, and reset pull-up. The VDD after the Imeasure jumper only connects to the
MCU.
5.8. Debug Header (J23)
The shrouded 10-pin debug header supports the Silicon Labs USB Debug Adapter. This connector provides a C2
debug connection to the C8051F85x/86x on the MCU card.
5.9. Reset Button (S5)
The reset push-button switch is just below the debug header (J23). Pushing this button will always reset the MCU.
Note that pushing this button while the IDE is connected to the MCU will result in the IDE disconnecting from the
target.
5.10. UART Connection Options (J7, U2, U4, U5)
The MCU card features a USB virtual COM port (VCP) UART connection via the mini-B USB connector (J5)
labeled COM PORT. The VCP connection uses the CP210x USB-to-UART bridge chip (U2). The GPIO pins
connected to the CP210x device can be enabled or disabled through the J7 header. Table 4 shows the GPIO pins
that are routed to the CP210x.
In addition to the CP210x USB-to-UART connection, the MCU card can connect the C8051F850 UART signals
with the UDP Motherboard UART signals UART_TX_SYS and UART_RX_SYS using U5. The signals to switch
between the two interfaces are UART_VCP_EN and UART_SYS_EN and are controlled by the motherboard. The
default selection with or without the motherboard is the CP210x VCP interface using a pull-down resistor R20.
Table 4. CP210x Controlled GPIO Pins
MCU Pin
P0.4
P0.5
VDD
COM Function
UART Transmit
UART Receive
COM VIO
5.11. Port Pin Headers (J24, J24, J26)
All of the MCU port pins are available on the 0.100-inch headers on MCU card. Each connector provides
connections to each port, VDD, and ground. Any unused pins on the P2 header are not connected. Some of these
port pins are shared with other functions on the board and may be modified as explained in Section 5.13.
Rev. 0.2
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