ST52T400 datasheet(48/94 Pages) STMICROELECTRONICS

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ST52T400/T440/E440/T441

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6.4 Alternate Functions.

Port A and B pins in ST52x400/440/441 are con-

figurabletobeusedwithdifferent functions (Alter-

nate Functions) related to the use of peripherals.

To configure a pin in Alternate Function the related

configuration registers must be set according to

the values shown in Tables - Port A - REG_CONF

4, - Port A - REG_CONF 12 and Analog Inputs

REG_CONF 14.

For example: if pin PA5/TCLK has to be used as

an external PWM/Timer Clock, REG_CONF4[(5)]

bit must be set to ‘1’.

When the signal is an input of an on-chip

peripheral, the related I/O pin has to be config-

ured in Input Mode.

When a pin of Port B is used as an Analog Input,

the related I/O pin is automatically set in threes-

tate. The analog multiplexer (controlled by the

Analog

Comparator

Configuration

switches the analog voltage present on the

selected pin to the common analog rail, which is

connected to the ADC input.

It is recommended that the voltage level or loading

on any port pin not be changed while conversion

is running. Furthermore, it is recommended not to

have clocking pins located close to a selected

analog pin.

6.5 I/O Port Configuration Registers

The I/O mode for each bit of the three ports are

selected by using Configuration Registers 4, 12,

13 and 11 (Table 6.1). The structure of these reg-

isters is illustrated in tables - Port A - REG_CONF

4, - Port A - REG_CONF 12, - Port B -

REG_CONF 13, Analog Inputs REG_CONF 14

and - Port C - REG_CONF 11. Each bit of the con-

figuration registers sets the I/O mode of the

related port pin.

Analog Comparator Inputs

Pins PB0-PB7 for ST52x440G/441G and PB0-

PB3 and PB7 in ST52x440F/441F can be config-

ured to be Analog Inputs by setting the related bit

in REG_CONF 14 to “1” (Table 6.7) and the

related bit in REG_CONF13 to “1” (Table 6.6).

These analog inputs are connected to the on chip

Analog Comparator.

If the BandGap Reference (BG) is needed as an

Output for ST52x440G/441G REG_CONF13[6]

must be set to “0” and REG_CONF14[6] to “1”.

Timer/PWM Alternate Functions

Pins of Port A can be configured to be I/Os of the

on-chip TIMER/PWM of ST52x400/440/441. The

configuration of these pins is performed by using

Configuration

Registers

REG_CONF4

and

REG_CONF12 (Tables - Port A - REG_CONF 4

and - Port A - REG_CONF 12).

If a pin has to be a TIMER Input

(TSTRT, TCLK,

TRES) the related bit of REG_CONF4 must be set

to “1” and of REG_CONF12 must be set to “1”.

If, instead it must be a TIMER Output (TOUT,

TOUTN), REG_CONF12 related bit must be set to

“0” and the related bit of REG_CONF4 be set to

“0”.

TRIAC Driver Alternate Function

When using the on-chip TRIAC, to have the

TRIAC Output on pin PA0, bit REG_CONF12[0]

must be set to “0” and REG_CONF4[0] to “0”.

When a synchronization with the Mains voltage is

necessary, in case either the Phase Angle Partial-

ization or the Burst Modes is chosen, to have

MAIN1 and MAIN2 as Inputs on PortA, it is neces-

sary to set bits 1 and2 of REG_CONF4to“1”.

(*) Not available in ST52x400xx

Table 6.4 -PortA -REG_CONF 4

Bit

Name

Value

Pin Description

0D0

PA0

PA1/MAIN1

PA2/MAIN2

PA3/ACSTRT(*)

PA4/TSTRT

PA5/TCLK

PA6/TRES

PA7/INT

X = 0 Pin set as Digital Output

X = 1 Pin set as Alternate Function Input

Reset Configuration ‘1111’

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