CY7C66013-PVC datasheet(14/58 Pages) CYPRESS

14 / 58 page

CY7C66013

CY7C66113

Document #: 38-08024 Rev. *A

Page 14 of 58

5.0

Programming Model

5.1

14-bit Program Counter (PC)

The 14-bit Program Counter (PC) allows access to up to 8 KB of PROM available with the CY7C66x13 architecture. The top 32

bytes of the ROM in the 8K part are reserved for testing purposes. The program counter is cleared during reset, such that the

first instruction executed after a reset is at address 0x0000h. Typically, this is a jump instruction to a reset handler that initializes

the application (see Section 16.1, Interrupt Vectors, on page 30).

The lower eight bits of the program counter are incremented as instructions are loaded and executed. The upper six bits of the

program counter are incremented by executing an XPAGE instruction. As a result, the last instruction executed within a 256-byte

“page” of sequential code should be an XPAGE instruction. The assembler directive “XPAGEON” causes the assembler to insert

XPAGE instructions automatically. Because instructions can be either one or two bytes long, the assembler may occasionally

need to insert a NOP followed by an XPAGE to execute correctly.

The address of the next instruction to be executed, the carry flag, and the zero flag are saved as two bytes on the program stack

during an interrupt acknowledge or a CALL instruction. The program counter, carry flag, and zero flag are restored from the

program stack during a RETI instruction. Only the program counter is restored during a RET instruction.

The program counter cannot be accessed directly by the firmware. The program stack can be examined by reading SRAM from

location 0x00 and up.

CY7C66013-PVC Datasheet(PDF) 14 Page - Cypress Semiconductor