ST52T430 datasheet(17/88 Pages) STMICROELECTRONICS

17 / 88 page

ST52T430/E430

17/88

The STACK POINTER indicates the first level

available to store data. When a subroutine call or

interrupt request occurs, the content of the PC and

the current set of flags are stored into the level

located by the STACK POINTER.

When a interrupt return occurs (RETI instruction),

the data stored in the highest stack level is

restored back into the PC and current flags.

Instead, when a subroutine return occurs (RET

instruction) the data stored in the highest stack

level are restored in the PC not affecting the flags.

These operating modes are illustrated in Figure

2.4.

Note:

The user must pay close attention to avoid

overwriting RAM locations where the STACK could

be stored.

2.3.2 Input Registers Bench.

The Input Registers (IR) bench consists of 20 8-bit

registers containing data or the status of the

peripherals.

All the registers can be specified by using a

decimal address (for example, 0 identifies the first

The assembler instruction:

LDRI RAM_Reg. IR_i

loads the value of the i-th IR in the RAM location

identified by the RAM_Reg address.

The first input register is dedicated to store the

value of the stack pointer. The next 8 registers

(ADC_OUT_0:7) of the IR are dedicated to the 8

converted values deriving from the ADC. The last

9 Input Registers contain data from the I/O ports

and PWM/Timers. The following table summarizes

the IR address and the relative peripherals. In

order to simplify the concept, a mnemonic name is

assigned to the registers. The same name is used

in VISUALSTUDIO® development tools

Figure 2.4 Stack Operation

PROGRAMCOUNTER

RAM

REG0

REG1

REG2

REG3

REG4

REG5

REG255

REG254

REG253

REG252

STACKLEVEL 1

STACKLEVEL 2

..........................

STACKLEVEL n

WHENCALL OR

INTERRUPT REQ.

WHENRETI ORRET

OCCURS

Stack

Pointer

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