ST92F124/F150/F250 - GENERAL DESCRIPTION
How to Configure the I/O Ports
To configure the I/O ports, use the information in
Table 3, Table 4 and the Port Bit Configuration Ta-
ble in the I/O Ports Chapter (See page 152).
Example 1: SCI-M input
AF: SIN, Port: P5.2. Schmitt Trigger input.
Write the port configuration bits:
P5C2.2=1
P5C1.2=0
P5C0.2 =1
Input Note = the hardware characteristics fixed for
each port line in Table 3.
– If Input note = TTL/CMOS, either TTL or CMOS
input level can be selected by software.
Enable the SCI peripheral by software as de-
scribed in the SCI chapter.
– If Input note = Schmitt trigger, selecting CMOS
or TTL input by software has no effect, the input
will always be Schmitt Trigger.
Example 2: SCI-M output
AF: SOUT, Port: P5.3, Push-Pull/OD output.
Write the port configuration bits (for AF OUT PP):
Alternate Functions (AF) = More than one AF
cannot be assigned to an I/O pin at the same time:
P5C2.3=0
P5C1.3=1
P5C0.3 =1
An alternate function can be selected as follows.
AF Inputs:
Example 3: External Memory I/O
– AF is selected implicitly by enabling the corre-
sponding peripheral. Exception to this are ADC
inputs which must be explicitly selected as AF in-
put by software.
AF: A0/D0, Port : P0.0, Input Note: TTL/CMOS in-
put.
Write the port configuration bits:
AF Outputs or Bidirectional Lines:
P0C2.0=1
P0C1.0=1
P0C0.0 =1
– In the case of Outputs or I/Os, AF is selected ex-
plicitly by software.
Example 4: Analog input
AF: AIN8, Port : 7.0, Analog input.
Write the port configuration bits:
P7C2.0=1
P7C1.0=1
P7C0.0 =1
24/426
9
STMICROELECTRONICS [ ST ]
