ST10F269Z1Q6 datasheet(60/184 Pages) STMICROELECTRONICS

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12 - PARALLEL PORTS

ST10F269

60/184

12.2.3 - Output Driver Control

The port output control registers POCONx allow

to select the port output driver characteristics of a

port. The aim of these selections is to adapt the

output drivers to the application’s requirements,

and to improve the EMI behaviour of the device.

Two characteristics may be selected:

Edge characteristic defines the rise/fall time for

the respective output. Slow edges reduce the

peak currents that are sinked/sourced when

changing

the

voltage

level

external

capacitive load. For a bus interface or pins that are

changing

frequency

higher

than

1MHz,

however, fast edges may still be required.

Driver characteristic defines either the general

driving capability of the respective driver, or if the

driver strength is reduced after the target output

level has been reached or not. Reducing the

driver strength increases the output’s internal

resistance,

which

attenuates

noise

that

imported via the output line. For driving LEDs or

power transistors, however, a stable high output

current may still be required as described below.

This rise / fall time of 4 I/O pads (a nibble) is

selected using 2-bit named PNxEC. That means

Port Nibble (x = nibble number, it could be 3 as for

Port 2.15 to 2.12) Edge Characteristic.

The sink / source capability of the same 4 I/O

pads is selected using 2-bit named PNxDC. That

means Port Nibble (x = nibble number) Drive

Characteristic (See Table 18).

POCONx (F0yyh / zzh) for 8-bit Ports

ESFR

Reset Value: --00h

POCONx (F0yyh / zzh) for 16-bit Ports

ESFR

ResetValue:0000h

Note: In case of reading an 8 bit P0CONX register, high Byte (bit 15..8) is read as 00h

Figure 20 : Hysteresis for Special Input Thresholds

Input level

Bit state

Hysteresis

9876543210

--------

PN1DC

PN1EC

PN0DC

PN0EC

9876543210

PN3DC

PN3EC

PN2DC

PN2EC

PN1DC

PN1EC

PN0DC

PN0EC

Bit

Function

PNxEC

Port Nibble x Edge Characteristic (rise/fall time)

00:

Fast edge mode, rise/fall times depend on the size of the driver.

01:

Slow edge mode, rise/fall times ~60 ns

10:

Reserved

11:

Reserved

PNxDC

Port Nibble x Driver Characteristic (output current)

00:

High Current mode:

Driver always operates with maximum strength.

01:

Dynamic Current mode:

Driver strength is reduced after the target level has been reached.

10:

Low Current mode:

Driver always operates with reduced strength.

11:

Reserved

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