C8051F120 Datasheet, PDF (255/356 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F120/1/2/3/4/5/6/7
C8051F130/1/2/3
contention between devices in systems where the Port pin participates in a shared interconnection in
which multiple outputs are connected to the same physical wire.
The output modes of the Port pins on Ports 4 through 7 are determined by the bits in their respective PnM-
DOUT Output Mode Registers. Each bit in PnMDOUT controls the output mode of its corresponding port
pin (see Figure 18.20, Figure 18.22, Figure 18.24, and Figure 18.27). For example, to place Port pin 4.3 in
push-pull mode (digital output), set P4MDOUT.3 to logic 1. All port pins default to open-drain mode upon
device reset.
18.2.3. Configuring Port Pins as Digital Inputs
A Port pin is configured as a digital input by setting its output mode to “Open-Drain” and writing a logic 1 to
the associated bit in the Port Data register. For example, P7.7 is configured as a digital input by setting
P7MDOUT.7 to a logic 0 and P7.7 to a logic 1.
18.2.4. Weak Pull-ups
By default, each Port pin has an internal weak pull-up device enabled which provides a resistive connec-
tion (about 100 kΩ) between the pin and VDD. The weak pull-up devices can be globally disabled by writ-
ing a logic 1 to the Weak Pull-up Disable bit, (WEAKPUD, XBR2.7). The weak pull-up is automatically
deactivated on any pin that is driving a logic 0; that is, an output pin will not contend with its own pull-up
device.
18.2.5. External Memory Interface
If the External Memory Interface (EMIF) is enabled on the High ports (Ports 4 through 7), EMIFLE
(XBR2.5) should be set to a logic 0.
If the External Memory Interface is enabled on the High ports and an off-chip MOVX operation occurs, the
External Memory Interface will control the output states of the affected Port pins during the execution
phase of the MOVX instruction, regardless of the settings of the Port Data registers. The output configura-
tion of the Port pins is not affected by the EMIF operation, except that Read operations will explicitly dis-
able the output drivers on the Data Bus during the MOVX execution. See Section “17. External Data
Memory Interface and On-Chip XRAM” on page 221 for more information about the External Memory Inter-
face.
Rev. 1.3
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