CRT Television User Manual

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ST92195B - GENERAL INFORMATION
1.2.2 I/O Port Styles
Legend:
AF= Alternate Function, BID = Bidirectional, OD = Open Drain
PP = Push-Pull, TTL = TTL Standard Input Levels
How to Read this Table
To configure the I/O ports, use the information in
this table and the Port Bit Configuration Table in
the I/O Ports Chapter on page 68.
Port Style
= the hardware characteristics fixed for
each port line.
Inputs:
– If port style = Standard I/O, either TTL or CMOS
input level can be selected by software.
– If port style = Schmitt trigger, selecting CMOS or
TTL input by software has no effect, the input will
always be Schmitt Trigger.
Weak Pull-Up
= This column indicates if a weak
pull-up is present or not.
– If WPU = yes, then the WPU can be enabled/dis-
able by software
– If WPU = no, then enabling the WPU by software
has no effect
Alternate Functions (AF)
= More than one AF
cannot be assigned to an external pin at the same
time:
An alternate function can be selected as follows.
AF Inputs:
– AF is selected implicitly by enabling the corre-
sponding peripheral. Exception to this are ADC
analog inputs which must be explicitly selected
as AF by software.
AF Outputs or Bidirectional Lines:
– In the case of Outputs or I/Os, AF is selected
explicitly by software.
Example 1: ADC trigger digital input
AF: EXTRG, Port: P4.7, Port Style: Standard I/O.
Write the port configuration bits (for TTL level):
P4C2.7=1
P4C1.7=0
P4C0.7=1
Enable the ADC trigger by software as described
in the ADC chapter.
Example 2: PWM 0 output
AF: PWM0, Port: P4.0
Write the port configuration bits (for output push-
pull):
P4C2.0=0
P4C1.0=1
P4C0.0=1
Example 3: ADC analog input
AF: AIN1, Port : P2.1, Port style: does not apply to
analog inputs
Write the port configuration bits:
P2C2.1=1
P2C1.1=1
P2C0.1=1
Pins Weak Pull-Up Port Style Reset Values
P0[7:0] no Standard I/O BID / OD / TTL
P2[5,4,3,2] no Standard I/O BID / OD / TTL
P2[1,0] no Schmitt trigger BID / OD / TTL
P3.7 yes Standard I/O AF / PP / TTL
P3[6,5,4] no Standard I/O BID / OD / TTL
P4[7:0] no Standard I/O BID / OD / TTL
P5[1:0] no Standard I/O BID / OD / TTL