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ST92141 - I/O PORTS

6.5 ALTERNATE FUNCTION ARCHITECTURE

Each I/O pin may be connected to three different

types of internal signal:

– Data bus Input/Output

– Alternate Function Input

– Alternate Function Output

6.5.1 Pin Declared as I/O

A pin declared as I/O, is connected to the I/O buff-

er. This pin may be an Input, an Output, or a bidi-

rectional I/O, depending on the value stored in

(PxC2, PxC1 and PxC0).

6.5.2 Pin Declared as an Alternate Function

Input

A single pin may be directly connected to several

Alternate Function inputs. In this case, the user

must select the required input mode (with the

PxC2, PxC1, PxC0 bits) and enable the selected

Alternate Function in the Control Register of the

peripheral. No specific port configuration is re-

quired to enable an Alternate Function input, since

the input buffer is directly connected to each alter-

nate function module on the shared pin. As more

than one module can use the same input, it is up to

the user software to enable the required module

as necessary. Parallel I/Os remain operational

even when using an Alternate Function input. The

exception to this is when an I/O port bit is perma-

nently assigned by hardware as an A/D bit. In this

case , after software programming of the bit in AF-

OD-TTL, the Alternate function output is forced to

logic level 1. The analog voltage level on the cor-

responding pin is directly input to the A/D (See Fig-

ure 48).

Figure 48. A/D Input Configuration

6.5.3 Pin Declared as an Alternate Function

Output

The user must select the AF OUT configuration

using the PxC2, PxC1, PxC0 bits. Several Alter-

nate Function outputs may drive a common pin. In

such case, the Alternate Function output signals

are logically ANDed before driving the common

pin. The user must therefore enable the required

Alternate Function Output by software.

WARNING: When a pin is connected both to an al-

ternate function output and to an alternate function

input, it should be noted that the output signal will

always be present on the alternate function input.

6.6 I/O STATUS AFTER WFI, HALT AND RESET

The status of the I/O ports during the Wait For In-

terrupt, Halt and Reset operational modes is

shown in the following table. The External Memory

Interface ports are shown separately. If only the in-

ternal memory is being used and the ports are act-

ing as I/O, the status is the same as shown for the

other I/O ports.

INPUT LATCH

INTERNAL DATA BUS

I/O PIN

TRISTATE

INPUT

BUFFER

OUTPUT SLAVE LATCH

OUTPUT MASTER LATCH

TOWARDS

A/D CONVERTER

GND

Mode

Ext. Mem - I/O Ports

I/O Ports

P1, P2,

P6, P9

WFI

High Imped-

ance or next

address (de-

pending on

the last

memory op-

eration per-

formed on

Port)

Address

Not Affected (clock

outputs running)

HALT

High Imped-

ance

Address

Not Affected (clock

outputs stopped)

RESET

Alternate function push-

pull (ROMless device)

Bidirectional Weak

Pull-up (High im-

pedance when disa-

bled in hardware).

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