ST92185B datasheet(16/178 Pages) STMICROELECTRONICS

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ST92185B - GENERAL DESCRIPTION

PIN DESCRIPTION (Cont’d)

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 69.

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]

Standard I/O

BID / OD / TTL

P2[5,4,3,2]

Standard I/O

BID / OD / TTL

P2[1,0]

Schmitt trigger

BID / OD / TTL

P3.7

yes

Standard I/O

AF / PP / TTL

P3[6,5,4]

Standard I/O

BID / OD / TTL

P4[7:0]

Standard I/O

BID / OD / TTL

P5[1:0]

Standard I/O

BID / OD / TTL

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