T410 datasheet(41/84 Pages) STMICROELECTRONICS

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ST52T410/ST52T420/E420

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7 I/O PORTS

7.1 Introduction

ST52T410/ST52x420

devices

feature

flexible

individually programmable multi-functional input/

output lines. Refer to the following figure for

specific pin allocations.

19 I/O lines, grouped in 3 different ports are

available on the ST52T410/ST52x420:

PORT A = 7 or 8-bit ports (PA0 - PA7 pins)

PORT B = 7 or 8-bit ports (PB0 - PB7 pins)

PORT C = 4-bit port (PC0 - PC3 pins)

PIN 18 can be configured to belong to port A or to

port B.

These I/O lines can be programmed to provide

digital input/output and analog input, or to connect

input/output signals to the on-chip peripherals as

alternate pin functions.

Input buffers are TTL compatible with Schmitt

trigger in port A and C while port B is CMOS

compatible without Schmitt trigger.

The output buffer can supply up to 8 mA.

The port cannot be configured to be used

contemporaneously as input and output.

Figure 7.1 Ports A & C Functional Blocks

Each port is configured by using two configuration

registers. The first is used to determine if a pin is

an input or output, while the second defines the

Alternate functions.

7.2 Input Mode

The input configuration is selected by setting the

corresponding configuration register bit to “1”

(REG_CONF 4, 13 and 15) (see paragraph I/O

Port Configuration Registers). The ports are

configured by using the configuration registers

illustrated in the following table.

Digital input data is automatically stored in the

Input Registers, but it cannot be read directly. In

order to read a single bit of the IR its value must be

copied in a RAM location. Digital data is stored in a

RAM location by using the assembler instruction:

LDRI RAM_Reg Input_i

Table 7.1 I/O Port Configuration Registers.

PORT A

PORT B

PORT C

Reg_Conf 4

Reg_Conf 13

Reg_Conf 15

TTL

PORT A PIN

or PORT C PIN

TO INPUT REGISTER

and PERIPHERALS

FROM PERIPHERAL

FROM OUTPUT REGISTER

FROM CONFIGURATION REGISTER

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