UPSD3313D-40T6 datasheet(59/231 Pages) STMICROELECTRONICS

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uPSD33xx

Alternate Functions. There are five SFRs used

to control the mapping of alternate functions onto

MCU port pins, and these SFRs are depicted as

switches in Figure 16., page 55.

■

Port 3 uses the SFR, P3SFS (Table

28., page 60).

■

Port 1 uses SFRs, P1SFS0 (Table

29., page 60) and P1SFS1 (Table

30., page 60).

■

Port 4 uses SFRs, P4SFS0 (Table

32., page 61) and P4SFS1 (Table

33., page 61).

Since these SFRs are cleared by a reset, then by

default all port pins function as GPIO (not the alter-

nate function) until firmware initializes these SFRs.

Each pin on each of the three ports can be inde-

pendently assigned a different function on a pin-

by-pin basis.

The peripheral functions Timer 2, UART1, and I2C

may be split independently between Port 1 and

Port 4 for additional flexibility by giving a wider

choice of peripheral usage on a limited number of

device pins.

When the selected alternate function is UART0,

UART1, or SPI, then the related pins are in quasi-

bidirectional mode, including the use of the high-

side driver for rapid 0-to-1 output transitions. The

high-side driver is enabled for just one MCU_CLK

period on 0-to-1 transitions by the delay function at

the “digital_alt_func_data_out” signal pictured in

Figure 17., page 56 through Figure 19., page 57.

If the alternate function is Timer 0, Timer 1, Timer

2, or PCA input, then the related pins are in quasi-

bidirectional mode, but input only.

If the alternate function is ADC, then for each pin

the pull-ups, the high-side driver, and the low-side

driver are disabled. The analog input is routed di-

rectly to the ADC unit. Only Port 1 supports analog

functions (Figure 17., page 56). Port 1 is not 5V

tolerant.

If the alternate function is I2C, the related pins will

be in open drain mode, which is just like quasi-bi-

directional mode but the high-side driver is not en-

abled for one cycle when 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., page 56). I2C re-

quires the use of an external pull-up resistor on

each bus signal, typically 4.7K

Ω to VCC.

If the alternate function is PCA output, then the re-

lated 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., page 57). 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

Port

(see

Table

129., page 207).

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

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