UPSD3422 datasheet(75/293 Pages) STMICROELECTRONICS

75 / 293 page

uPSD34xx

I/O ports of mcu module

75/293

outputting a 0-to-1 transition. Only the low-side driver and the internal weak pull-ups are

used. Only Port 3 supports open-drain mode (Figure 18 on page 72). I2C requires the use of

an external pull-up resistor on each bus signal, typically 4.7K

Ω to V

CC.

If the alternate function is PCA output, then the related pins are in push-pull mode, meaning

the pins are actively driven and held to logic '1' by the high-side driver, or actively driven and

held to logic '0' by the low-side driver. Only Port 4 supports push-pull mode (Figure 19 on

page 72). Port 4 push-pull pins can source IOH current when driving logic '1,' and sink IOL

current when driving logic '0.' This current is significantly more than the capability of pins on

Port 1 or Port 3 (see Table 156 on page 265).

For example, to assign these port functions:

●

Port 1: UART1, ADC[1:0], P1[7:4] are GPIO

●

Port 3: UART0, I2C, P3[5:2] are GPIO

●

Port 4: TCM0, SPI, P4[3:1] are GPIO

The following values need to be written to the SFRs:

P1SFS0 = 00001111b, or 0Fh

P1SFS1 = 00000011b , or 03h

P3SFS = 11000011b, or C3h

P4SFS0 = 11110001b, or F1h

P4SFS1 = 11110000b, or F0h

Table 30.

P3SFS: Port 3 Special Function Select Register (SFR 91h, reset value

00h)

Table 31.

P1SFS0: Port 1 Special Function Select 0 Register (SFR 8Eh, reset value

00h)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

P3SFS7

P3SFS6

P3SFS5

P3SFS4

P3SFS3

P3SFS2

P3SFS1

P3SFS0

Port 3 Pin

R/W

Default Port Function

Alternate Port Function

P3SFS[i] - 0; Port 3 Pin, i = 0..7

P3SFS[i] - 1; Port 3 Pin, i = 0..7

R,W

GPIO

UART0 Receive, RXD0

R,W

GPIO

UART0 Transmit, TXD0

R,W

GPIO

Ext Intr 0/Timer 0 Gate,

EXT0INT/TG0

R,W

GPIO

Ext Intr 1/Timer 1 Gate,

EXT1INT/TG1

R,W

GPIO

Counter 0 Input, C0

R,W

GPIO

Counter 0 Input, C1

R,W

GPIO

I2C Data, I2CSDA

R,W

GPIO

I2C Clock, I2CCL

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

P1SF07

P1SF06

P1SF05

P1SF04

P1SF03

P1SF02

P1SF01

P1SF00

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