ZLR64400ROMMCU datasheet(47/155 Pages) ZILOG

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PS024502-1205

P R E L I M I N A R Y

User Data Register

ZLR64400 ROM MCU

Product Specification

User Data Register

Bank-independent register FEh is available for user data storage. See Table 17.

Do not use register FEh as a counter for the DJNZ instruction.

Stack Pointer Register

The Stack Pointer register contains the 8-bit address of the stack pointer. The stack pointer

resides in Bank 0 of RAM. The stack address is decremented prior to a PUSH operation and

incremented after a POP operation. The stack address always points to the data stored at the

top of the stack (the lowest stack address). During a call instruction, the contents of the Pro-

gram Counter are saved on the stack. Interrupts cause the contents of the Program Counter

and Flags registers to be saved on the stack. An overflow or underflow can occur when the

stack address is incremented or decremented during normal operations. The programmer

must prevent this occurrence or unpredictable operations will result. See Table 18.

Table 17. User Data Register (USER)

Bit

Field

User Data

Reset

R/W

Address

Bank Independent: FEh; Linear: 0FEh

Bit

Position

Value

Description

[7:0]

00hFFh User Data

Table 18. Stack Pointer Register (SPL)

Bit

Field

Stack Pointer

Reset

R/W

Address

Bank Independent: FFh; Linear: 0FFh

Bit

Position Description

[7:0]

Stack Pointer

Note:

ZLR64400ROMMCU Datasheet(PDF) 47 Page - Zilog, Inc.

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