ade7566 Analog Devices, Inc., ade7566 Datasheet - Page 72

• Manufacturer Part Number: ade7566
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc, And Lcd Driver
• Manufacturer: Analog Devices, Inc.

ADE7566/ADE7569
BASIC 8052 REGISTERS
Program Counter (PC)
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 1 byte
to 3 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.
Instruction Register (IR)
The instruction register holds the opcode of the instruction
being executed. The opcode is the binary code that results from
assembling an instruction. This register is not directly accessible
to the user.
Register Banks
There are four banks that each contain 8 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 1 clock
cycle, as opposed to 2 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 active register bank is selected by the RS0 and RS1 bits in
the Program Status Word SFR (PSW, 0xD0).
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 54).
B Register
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 54).
Program Status Word (PSW)
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
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bits are described in Table 55. The Program Status Word SFR
(PSW, 0xD0) is bit addressable.
Data Pointer (DPTR)
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 Table 57 and Table 58.
The ADE7566/ADE7569 support dual data pointers. See the
Dual Data Pointers section.
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 of 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.
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 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.
Data can still be stored in XRAM by using the MOVX command.
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:
MOV
0xFF
0x00
SP,#00H
256 BYTES OF
(DATA)
RAM
Figure 76. Extended Stack Pointer Operation
0xFF
0x00
ON-CHIP XRAM
DATA + STACK
256 BYTES OF