Datasheet

ADE5166/ADE5169/ADE5566/ADE5569 Data Sheet
Rev. D | Page 82 of 156
Bit Mnemonic Default Description
4 MOD38EN 0 38 kHz modulation enable bit.
MOD38EN
Result
0 38 kHz modulation is disabled
1 38 kHz modulation is enabled on the pins selected by the MOD38 bits in the
EPCFG SFR (Address 0x9F[7:0])
[3:2] Reserved 00 Reserved. These bits should be kept at 0 for proper operation.
[1:0] XREN1,
XREN0
01
XREN1, XREN0 Result
XREN1 or XREN0 = 1 Enable MOVX instruction to use 256 bytes of extended RAM
XREN1 and XREN0 = 0 Disable MOVX instruction
BASIC 8052 REGISTERS
Program Counter (PC)
The program counter holds the 2-byte address of the next instruc-
tion to be fetched. The PC is initialized with 0x00 at reset and is
incremented after each instruction is performed. Note that the
amount that is added to the PC depends on the number of bytes
in the instruction; therefore, the increment can range from one
to three bytes. The program counter is not directly accessible to
the user but can be directly modified by CALL and JMP instruc-
tions 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 assem-
bling an instruction. This register is not directly accessible to
the user.
Register Banks
There are four banks, each containing an 8-byte-wide register, for
a total of 32 bytes of registers. These registers are convenient for
temporary storage of mathematical operands. An instruction in-
volving 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 active register bank is selected by RS0 and RS1 in the
program status wo r d S F R ( P S W, Address 0xD0[4:3]).
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 word SFR (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 57).
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 it
is not used for many instructions, it can be used as a scratch pad
register like those in the register banks. The B register is stored
in the SFR space (see Table 57).
Program Status Word (PSW)
The PSW SFR (PSW, Address 0xD0) reflects the status of
arithmetic and logical operations through carry, auxiliary carry,
and overflow flags. The parity flag reflects the parity of the contents
of the accumulator, which can be helpful for communication
protocols. The program status word SFR is bit addressable (see
Table 58).
Data Pointer (DPTR)
The data pointer SFR (DPTR, Address 0x82 and Address 0x83)
is made up of two 8-bit registers: DPL (low byte, Address 0x82),
and DPH (high byte, Address 0x83). These SFRs 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 and DPL) (see Table 60 and
Table 61).
The 8052 MCU core architecture supports dual data pointers
(see the 8052 MCU Core Architecture section).
Stack Pointer (SP)
The stack pointer SFR (SP, Address 0x81) keeps track of the
current address of 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 uses 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 used 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.