ST52T430 datasheet(16/88 Pages) STMICROELECTRONICS

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ST52T430/E430

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The ST52x430 core uses flags that correspond to

the actual mode. As soon as an interrupt is

generated the ST52x430 core uses the interrupt

flags instead of the normal flags.

Each interrupt level has its own set of flags, which

is saved in the STACK together with the Program

Counter. These flags are restored from the STACK

automatically when a RETI instruction is executed.

If the MCU was in normal mode before an interrupt,

the normal flags are restored when the RETI

instruction is executed.

Note:

A CALL subroutine is a normal mode

execution. For this reason, a RET instruction,

consequent to a CALL instruction does not affect

the normal mode set of flags.

Flags are not cleared during context switching and

remain in the state they were at the end of the last

interrupt routine switching.

The Carry flag is set when an overflow occurs

during arithmetic operations, otherwise it

cleared.

The Sign flag is set when an underflow occurs

during

arithmetic

operations,

otherwise

it is

cleared.

2.3 Address Spaces

ST52x430 has four separate address spaces:

RAM: 256 Bytes

Figure 2.3 Address Spaces Description

Input Registers: 20 8-bit registers

Output Registers 10 8-bit registers

Configuration Registers: 21 8-bit registers

Program memory up to 8K Bytes

Program memory will be described in further

details in the MEMORY section

2.3.1 RAM and STACK.

RAM memory consists of 256 general purpose 8-

bit RAM registers.

All the registers in RAM can be specified by using

a decimal address. For example, 0 identifies the

first register of RAM.

To read or write RAM registers LOAD instructions

must be used. See Table 2.5

Each interrupt level has its own set of flags, which

is saved in the STACK together with the Program

Counter. These flags are restored from the STACK

automatically when a RETI instruction is executed.

When the instructions like Interrupt request or

CALL are executed, a STACK level is used to push

the PC.

The STACK is located in RAM. For each level of

stack, 2 bytes of RAM are used. The values of this

stack are stored from the last RAM register

(address 255). The maximum level of stack

must be less than 128.

ST52X430 CORE

PROGRAM MEMORY

RAM

CONTROL UNIT

DPU

ALU

ON CHIP PERIPHERALS

PERIPHERAL REGISTERS

CONFIGURATION

REGISTERS

INPUT REGISTERS

LDRI

LDCR

LDPR

LDRC

LDCE

PERIPHERAL

BLOCK

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