PSD834F2V datasheet(49/89 Pages) STMICROELECTRONICS

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PSD834F2V

Direction Register. The Direction Register, in

conjunction with the output enable (except for Port

D), controls the direction of data flow in the I/O

Ports. Any bit set to 1 in the Direction Register

causes the corresponding pin to be an output, and

any bit set to 0 causes it to be an input. The default

mode for all port pins is input.

Table 22. Port Pin Direction Control, Output

Enable P.T. Not Defined

Table 23. Port Pin Direction Control, Output

Enable P.T. Defined

Table 24. Port Direction Assignment Example

Figure 25 and Figure 26 show the Port Architec-

ture diagrams for Ports A/B and C, respectively.

The direction of data flow for Ports A, B, and C are

controlled not only by the direction register, but

also by the output enable product term from the

PLD AND Array. If the output enable product term

is not active, the Direction Register has sole con-

trol of a given pin’s direction.

An example of a configuration for a Port with the

three least significant bits set to output and the re-

mainder set to input is shown in Table 24. Since

Port D only contains three pins (shown in Figure

28), the Direction Register for Port D has only the

three least significant bits active.

Drive Select Register. The Drive Select Register

configures the pin driver as Open Drain or CMOS

for some port pins, and controls the slew rate for

the other port pins. An external pull-up resistor

should be used for pins configured as Open Drain.

A pin can be configured as Open Drain if its corre-

sponding bit in the Drive Select Register is set to a

1. The default pin drive is CMOS.

Note that the slew rate is a measurement of the

rise and fall times of an output. A higher slew rate

means a faster output response and may create

more electrical noise. A pin operates in a high slew

rate when the corresponding bit in the Drive Reg-

ister is set to 1. The default rate is slow slew.

Table 25 shows the Drive Register for Ports A, B,

C, and D. It summarizes which pins can be config-

ured as Open Drain outputs and which pins the

slew rate can be set for.

Port Data Registers

The Port Data Registers, shown in Table 26, are

used by the MCU to write data to or read data from

the ports. Table 26 shows the register name, the

ports having each register type, and MCU access

for each register type. The registers are described

below.

Table 25. Drive Register Pin Assignment

Note: 1. NA = Not Applicable.

Direction Register Bit

Port Pin Mode

Input

Output

Direction

Output Enable

P.T.

Port Pin Mode

Input

Output

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Drive

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Port A

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Slew

Rate

Slew

Rate

Slew

Rate

Slew

Rate

Port B

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Slew

Rate

Slew

Rate

Slew

Rate

Slew

Rate

Port C

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Open

Drain

Port D

NA1

Slew

Rate

Slew

Rate

Slew

Rate

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