AN2555 - Application note

Modified features

14/33

1.7

Port input control

The Port Input Control register PICON is used to select between TTL and CMOS-like input thresholds.

The CMOS-like input thresholds are defined above the TTL levels and feature a hysteresis to prevent the

inputs from toggling while the respective input signal level is near the thresholds.

On the ST10F269Zx this feature is available for all pins of Port 2, Port 3, Port4, Port 7 and Port 8 and the

hysteresis level is 250mV for CMOS levels.

In the ST10F276Z5, Port 6 has been added. Moreover the default hysteresis is now 500mV for TTL levels

and 800mV for CMOS levels.

ESFR

Reset Value: --00h

ESFR

Reset Value: --00h

1.7.1

Hardware impacts

The CMOS levels of the 2 devices are slightly different, therefore the circuitry must be checked to verify

that the new levels can still match the requirements. Refer to the ST10F276Z5 datasheet and to the

Section 5.1: DC characteristics for more details.

1.7.2

Software impacts

The initialization of the PICON register should be checked to control that it is not writing to the new bit

P6LIN.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

---

---

--

P8LIN P7LIN

-

P4LIN P3HIN P3LIN P2HIN P2LIN

RW

RW

-

RW

RWRWRWRW

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

---

--

---

P8LIN P7LIN P6LIN P4LIN P3HIN P3LIN P2HIN P2LIN

RW

RW

RW

RW

RW

RW

RW

RW

Bit

Function

Reset Value

PxLIN

Port x Low Byte Input Level Selection

‘0’:

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

1:

Pins Px.7..0 switch on CMOS input levels

0

PxHIN

Port x High Byte Input Level Selection

‘0’:

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

‘1’:

Pins Px.15..8 switch on CMOS input levels

0