ST10F280_12 datasheet(96/239 Pages) STMICROELECTRONICS

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Parallel ports

ST10F280

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Doc ID 8673 Rev. 3

12.1.2

Input threshold control

The standard inputs of the ST10F280 determine the status of input signals according to TTL

levels. In order to accept and recognize noisy signals, CMOS-like input thresholds can be

selected instead of the standard TTL thresholds for all pins of Port 2, Port 3, Port4, Port 7

and Port 8. These special thresholds are defined above the TTL thresholds and feature a

defined hysteresis to prevent the inputs from toggling while the respective input signal level

is near the thresholds.

The Port Input Control register PICON is used to select these thresholds for each byte of the

indicated ports, i.e. the 8-bit ports P7 and P8 are controlled by one bit each while ports P2

and P3 are controlled by two bits each.

PICON

Address:

0xF1C4h / E2h ESFR

Reset:

0x--00h

Type:

R/W

All options for individual direction and output mode control are available for each pin,

independent of the selected input threshold. The input hysteresis provides stable inputs

from noisy or slowly changing external signals.

Figure 28.

Hysteresis for special input thresholds

12.1.3

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:

P8LIN P7LIN

P4LIN P3HIN P3LIN P2HIN P2LIN

R/W

PxLIN Port x Low Byte Input Level Selection

0: Pins Px.7...Px.0 switch on standard TTL input levels

1: Pins Px.7...Px.0 switch on special threshold input levels

PxHIN Port x High Byte Input Level Selection

0: Pins Px.15...Px.8 switch on standard TTL input levels

1: Pins Px.15...Px.8 switch on special threshold input levels

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