ST92F250CV2 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST92F250CV2

8/16-bit single voltage Flash MCU family with RAM, E³ TM (emulated EEPROM), CAN 2.0B and J1850 BLPD

STMicroelectronics 

ST92F124xx/ST92F150Cxx/ST92F150JDV1/ST92F250CV2

Device architecture

Note:

themselves automatically changed by the push or pop instruction, thus corrupting their

value.

System Stack

The System Stack is used for the temporary storage of system and/or control data, such as

the Flag register and the Program counter.

The following automatically push data onto the System Stack:

● Interrupts

When entering an interrupt, the PC and the Flag Register are pushed onto the System

Stack. If the ENCSR bit in the EMR2 register is set, then the Code Segment Register is

also pushed onto the System Stack.

● Subroutine Calls

When a call instruction is executed, only the PC is pushed onto stack, whereas when

a calls instruction (call segment) is executed, both the PC and the Code Segment

Register are pushed onto the System Stack.

● Link Instruction

The link or linku instructions create a C language stack frame of user-defined

length in the System or User Stack.

All of the above conditions are associated with their counterparts, such as return

instructions, which pop the stored data items off the stack.

1. User Stack

The User Stack provides a totally user-controlled stacking area.

The User Stack Pointer consists of two registers, R236 and R237, which are both used for

addressing a stack in memory. When stacking in the Register File, the User Stack Pointer

High Register, R236, becomes redundant but must be considered as reserved.

Stack Pointers

Both System and User stacks are pointed to by double-byte stack pointers. Stacks may be

set up in RAM or in the Register File. Only the lower byte will be required if the stack is in the

Register File. The upper byte must then be considered as reserved and must not be used as

a general purpose register.

The stack pointer registers are located in the System Group of the Register File, this is

illustrated in Table 8.

Stack Location

Care is necessary when managing stacks as there is no limit to stack sizes apart from the

bottom of any address space in which the stack is placed. Consequently programmers are

advised to use a stack pointer value as high as possible, particularly when using the

Register File as a stacking area.

Group D is a good location for a stack in the Register File, since it is the highest available

area. The stacks may be located anywhere in the first 14 groups of the Register File

(internal stacks) or in RAM (external stacks).

Stacks must not be located in the Paged Register Group or in the System Register Group.

Doc ID 8848 Rev 7

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