Interfacing Port I/O To 5 V Logic; Assigning Port I/O Pins To Analog And Digital Functions; Assigning Port I/O Pins To Analog Functions; Assigning Port I/O Pins To Digital Functions - Silicon Laboratories C8051T620 Manual

C8051T620/1/6/7 & C8051T320/1/2/3

22.1.3. Interfacing Port I/O to 5 V Logic

All Port I/O configured for digital, open-drain operation are capable of interfacing to digital logic operating at
a supply voltage higher than V
age is typically required for most systems.
Important Note: In a multi-voltage interface, the external pull-up resistor should be sized to allow a current
of at least 150uA to flow into the Port pin when the supply voltage is between (V
1.0V). Once the Port pin voltage increases beyond this range, the current flowing into the Port pin is mini-
mal.

22.2. Assigning Port I/O Pins to Analog and Digital Functions

Port I/O pins can be assigned to various analog, digital, and external interrupt functions. The Port pins
assigned to analog functions should be configured for analog I/O, and Port pins assigned to digital or exter-
nal interrupt functions should be configured for digital I/O.

22.2.1. Assigning Port I/O Pins to Analog Functions

Table 22.1 shows all available analog functions that require Port I/O assignments. Port pins selected for
these analog functions should have their corresponding bit in PnSKIP set to 1. This reserves the pin
for use by the analog function and does not allow it to be claimed by the Crossbar. Table 22.1 shows the
potential mapping of Port I/O to each analog function.
Table 22.1. Port I/O Assignment for Analog Functions
Analog Function
ADC Input
Comparator Input
Voltage Reference (VREF0)
External Oscillator in Crystal Mode (XTAL1, XTAL2)
External Oscillator in RC or C Mode (XTAL2)

22.2.2. Assigning Port I/O Pins to Digital Functions

Any Port pins not assigned to analog functions may be assigned to digital functions or used as GPIO. Most
digital functions rely on the Crossbar for pin assignment; however, some digital functions bypass the
Crossbar in a manner similar to the analog functions listed above. Port pins used by these digital func-
tions and any Port pins selected for use as GPIO should have their corresponding bit in PnSKIP set
to 1. Table 22.2 shows all available digital functions and the potential mapping of Port I/O to each digital
function.
140
and less than 5.25V. An external pull-up resistor to the higher supply volt-
IO
Rev. 1.2
Potentially Assignable
Port Pins
P0.0, P0.1, P0.4, P0.5,
P1.0- P3.0
P0.0, P0.1, P0.4, P0.5,
P1.0-P1.7, P2.0-P2.5
P0.7
P0.2, P0.3
P0.3
+ 0.6V) and (V +
IO IO
Suffers) used for
Assignment
AMX0P, PnSKIP
CPT0MX, CPT1MX,
PnSKIP
REF0CN, PnSKIP
OSCXCN, PnSKIP
OSCXCN, PnSKIP