Zilog Z16F2810 Manual de usuario descargar pdf (Pagina 122)

ILL Instruction UM018809-0611

106

ZNEO

CPU Core

User Manual

ILL

Definition

Illegal Instruction

Operation

SP  SP

– 2

(SP)  {00H, FLAGS[7:0]}

SP  SP

– 4

(SP)  PC

PC  (0000_0008H)

Description

This operation is performed whenever the CPU encounters an unimplemented instruction.

Because an unprogrammed memory element typically contains FFH, the opcode FFFFH (ILL) is

defined as an explicit Illegal Instruction Exception.

When the Program Counter encounters an illegal instruction, the Flags and Program Counter

value are pushed on the stack. The Program Counter does not increment, so the Program Counter

value that is pushed onto the stack points to the illegal instruction.

The ILL exception uses the System Exception vector quad at

0000_0008H in memory. The vec-

tor quad contains a 32-bit address (service routine pointer). When an exception occurs, the

address in the vector quad replaces the value in the Program Counter (PC). Program execution

continues with the instruction pointed to by the new PC value.

After an ILL exception occurs, the

ILL bit in the System Exception register (SYSEXCP) is set to

1. After the first ILL exception has executed, additional ILL exceptions do not push the Stack

Pointer until the

ILL bit is cleared. Writing a 1 to the ILL bit clears the bit to 0.

Refer to the ZNEO product specification that is specific to your device for detailed infor-

mation regarding the System Exception register (SYSEXCP).

The Break opcode (BRK, 00H) operates as an ILL exception if On-Chip Debugger breaks

are disabled. For details about the On-Chip Debugger, see the device-specific Product

Specification.

Note:

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Zilog Z16F2810 Manual de usuario Pagina 122