SX20AC75 datasheet(7/52 Pages) ETC

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SX18AC/SX20AC/SX28AC/SX18AC75/SX20AC75/SX28AC75

3.0

PORT DESCRIPTIONS

The device contains a 4-bit I/O port (Port A) and two 8-bit

I/O ports (Port B, Port C). Port A provides symmetrical

drive capability. Each port has three associated 8-bit reg-

isters (Direction, Data, TTL/CMOS Select, and Pull-Up

Enable) to configure each port pin as Hi-Z input or output,

to select TTL or CMOS voltage levels, and to enable/dis-

able the weak pull-up resistor. The upper four bits of the

registers associated with Port A are not used. The least

significant bit of the registers corresponds to the least

significant port pin. To access these registers, an appro-

priate value must be written into the MODE register.

Upon power-up, all bits in these registers are initialized to

“1”.

The associated registers allow for each port bit to be indi-

vidually configured under software control as shown

below:

3.1

Reading and Writing the Ports

The three ports are memory-mapped into the data mem-

ory address space. To the CPU, the three ports are avail-

able as the RA, RB, and RC file registers at data memory

addresses 05h, 06h, and 07h, respectively.

Writing to a port data register sets the voltage levels of

the corresponding port pins that have been configured to

operate as outputs. Reading from a register reads the

voltage levels of the corresponding port pins that have

been configured as inputs.

Table 3-1. Port Configuration

Data Direction

Registers:

RA, RB, RC

TTL/CMOS

Select Registers:

LVL_A, LVL_B,

LVL_C

Pullup Enable

Registers:

PLP_A, PLP_B,

PLP_C

010101

Output

Hi-Z

Input

CMOS

TTL

Enable

Disable

Figure 3-1. Port A Configuration

MODE

RA Data

LVL_A

0 = Output

1 = Hi-Z Input

0 = CMOS

1 = TTL

TTL Buffer

CMOS Buffer

Vdd

Pullup

Port A PIN

Direction

PLP_A

0 = Pullup Enable

1 = Pullup Disable

Port A INPUT

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