Cypress CY7C65113C manual bit Accumulator a, bit Temporary Register, bit Program Stack Pointer PSP

CY7C65113C

5.28-bit Accumulator (A)

The accumulator is the general-purpose register for the microcontroller.

5.38-bit Temporary Register (X)

The “X” register is available to the firmware for temporary storage of intermediate results. The microcontroller can perform indexed operations based on the value in X. Refer to Section 5.6.3 for additional information.

5.48-bit Program Stack Pointer (PSP)

During a reset, the Program Stack Pointer (PSP) is set to 0x00 and “grows” upward from this address. The PSP may be set by firmware, using the MOV PSP,A instruction. The PSP supports interrupt service under hardware control and CALL, RET, and RETI instructions under firmware control. The PSP is not readable by the firmware.

During an interrupt acknowledge, interrupts are disabled and the 14-bit program counter, carry flag, and zero flag are written as two bytes of data memory. The first byte is stored in the memory addressed by the PSP, then the PSP is incremented. The second byte is stored in memory addressed by the PSP, and the PSP is incremented again. The overall effect is to store the program counter and flags on the program “stack” and increment the PSP by two.

The Return From Interrupt (RETI) instruction decrements the PSP, then restores the second byte from memory addressed by the PSP. The PSP is decremented again and the first byte is restored from memory addressed by the PSP. After the program counter and flags have been restored from stack, the interrupts are enabled. The overall effect is to restore the program counter and flags from the program stack, decrement the PSP by two, and re-enable interrupts.

The Call Subroutine (CALL) instruction stores the program counter and flags on the program stack and increments the PSP by two.

The Return From Subroutine (RET) instruction restores the program counter but not the flags from the program stack and decrements the PSP by two.

5.4.1Data Memory Organization

The CY7C65113C microcontrollers provide 256 bytes of data RAM. Normally, the SRAM is partitioned into four areas: program stack, user variables, data stack, and USB endpoint FIFOs. The following is one example of where the program stack, data stack, and user variables areas could be located.

After reset

8-bit DSP 8-bit PSP

(Move DSP[1])

8-bit DSP

Address

0x00

user selected

0xFF

Program Stack Growth

Data Stack Growth

User variables

USB FIFO space for up to two Addresses and five endpoints[2]

Notes:

1.Refer to Section 5.5 for a description of DSP.

2.Endpoint sizes are fixed by the Endpoint Size Bit (I/O register 0x1F, Bit 7). See Table 17-1.

Document #: 38-08002 Rev. *D Page 13 of 49

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