ADE7166 datasheet(80/144 Pages) AD

80 / 144 page

ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 80 of 144

BASIC 8052 REGISTERS

Data Pointer (DPTR)

Program Counter (PC)

The data pointer is made up of two 8-bit registers: DPH (high

byte) and DPL (low byte). These provide memory addresses for

internal code and data access. The DPTR can be manipulated as

a 16-bit register (DPTR = DPH, DPL) or as two independent

8-bit registers (DPH, DPL). See

The program counter holds the two byte address of the next

instruction to be fetched. The PC is initialized with 0x00 at reset

and is incremented after each instruction is performed. Note

that the amount added to the PC depends on the number of

bytes in the instruction, so the increment can range from one

byte to three bytes. The program counter is not directly accessible

to the user but can be directly modified by CALL and JMP

instructions that change which part of the program is active.

Table 58 and Table 59.

The ADE7566/ADE7569/ADE7166/ADE7169 support dual

data pointers. See the Dual Data Pointers section. Note that the

Dual Data Pointers section of the data sheet is the only place

where the main and shadow data pointers are distinguished.

Whenever the data pointer (DPTR) is mentioned elsewhere in

the data sheet, active DPTR is implied.

Instruction Register (IR)

The instruction register holds the operations code of the

instruction being executed. The operations code is the binary

code that results from assembling an instruction. This register is

not directly accessible to the user.

Stack Pointer (SP)

The stack pointer keeps track of the current address at the top

of the stack. To push a byte of data onto the stack, the stack

pointer is incremented and the data is moved to the new top of

the stack. To pop a byte of data off the stack, the top byte of data

is moved into the awaiting address, and the stack pointer is

decremented. The stack is a last in, first out (LIFO) method of

data storage because the most recent addition to the stack is the

first to come off it.

There are four banks that each contain eight byte-wide registers

for a total of 32 bytes of registers. These registers are convenient

for temporary storage of mathematical operands. An

instruction involving the accumulator and a register can be

executed in one clock cycle, as opposed to two clock cycles to

perform an instruction involving the accumulator and a literal or

a byte of general-purpose RAM. The register banks are located in

the first 32 bytes of RAM.

The stack is utilized during CALL and RET instructions to keep

track of the address to move into the PC when returning from

the function call. The stack is also manipulated when vectoring

for interrupts to keep track of the prior state of the PC.

The active register bank is selected by the RS0 and RS1 bits in

the Program Status Word SFR (PSW, 0xD0).

The stack resides in the internal extended RAM, and the

SP register holds the address of the stack in the extended RAM

(XRAM). The advantage of this solution is that the stack is

segregated to the internal XRAM. The use of the general-

purpose RAM can be limited to data storage, and the use of the

extended internal RAM can be limited to the stack pointer. This

separation limits the chance of data RAM corruption when the

stack pointer overflows in data RAM.

Accumulator

The accumulator is a working register, storing the results of

many arithmetic or logical operations. The accumulator is used

in more than half of the 8052 instructions where it is usually

referred to as “A.” The program status register (PSW) constantly

monitors the number of bits that are set in the accumulator to

determine if it has even or odd parity. The accumulator is stored

in the SFR space (see Table 55).

Data can still be stored in XRAM by using the MOVX command.

B Register

0x00

0xFF

0x00

256 BYTES OF

ON-CHIP XRAM

DATA + STACK

256 BYTES OF

RAM

(DATA)

The B register is used by the multiply and divide instructions,

MUL AB and DIV AB to hold one of the operands. Because

the B register is not used for many instructions, it can be used

as a scratch pad register such as those in the register banks.

The B register is stored in the SFR space (see Table 55).

Program Status Word (PSW)

Figure 81. Extended Stack Pointer Operation

The PSW register reflects the status of arithmetic and logical

operations through carry, auxiliary carry, and overflow flags.

The parity flag reflects the parity of the accumulator contents,

which can be helpful for communication protocols. The PSW

bits are described in

To change the default starting address for the stack, move a

value into the stack pointer (SP). For example, to enable the

extended stack pointer and initialize it at the beginning of the

XRAM space, use the following code:

Table 56. The Program Status Word SFR

(PSW, 0xD0) is bit addressable.

MOV

SP,#00H

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