Page 72 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

blocks. The first 128 bytes of internal data memory are both directly and indirectly addressable. The upper 128
bytes of data memory (from 0x80 to 0xFF) can be addressed only indirectly.
Since internal data memory is used for CALL stack also and there are only 256 bytes splinted over a few different
memory areas, fine utilizing of this memory is crucial for fast and compact code. See types efficiency also.
Memory block in the range of 20h to 2Fh is bit-addressable, which means that each bit being there has its own
address from 0 to 7Fh. Since there are 16 such registers, this block contains a total of 128 bits with separate
addresses (Bit 0 of byte 20h has the bit address 0, and bit 7 of byte 2Fh has the bit address 7Fh).
Three memory type specifiers can be used to refer to the internal data memory: data, idata, and bdata.
External Data Memory
Access to external memory is slower than access to internal data memory. There may be up to 64K Bytes
of external data memory. Several 8051 devices provide on-chip XRAM space that is accessed with the same
instructions as the traditional external data space. This XRAM space is typically enabled via proper setting of SFR
register and overlaps the external memory space. The setting of that register must be manually done in code,
before any access to external memory or XRAM space is made.

The micro-PRO for 8051 has two memory type specifiers that refers to external memory space: xdata and pdata.

8051 Microcontroller Hardware

The 8051 architecture consists of these specific features:
Eight-bit CPU with:
Register A (the Accumulator)
Register B
Instruction set
Sixteen-bit program counter (PC) and data pointer (DPTR)
Eight-bit program status (PSW)

Eight-bit stack pointer (SP)
Internal ROM or EPROM (8751) of 0(8031) to 4K (8051)
Internal RAM of 128 bytes:
Four register banks, each containing eight registers

Sixteen bits, which may be addressed at the bit level:
128 addressable bits
Eighty bytes of general-purpose data memory
Thirty-two input/output pins arranged as four 8-bit ports: P0-P3
Two 16-bit timer/counters: T0 and T1

Full duplex serial data receiver/transmitter: SBUF
Control registers:
TCON
TMOD
SCON

PCON
IP
IE

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CITS : E & H - Electronics Mechanic - Lesson 34 - 42