1. Intel 8051
Another family of microcontroller is the Intel 8051 family. The basic 8051 microcontroller has four parallel input/output ports, port 0, 1, 2 and 3. The 8051AH version has 4K x 8 bytes ROM , 128 x 8 bytes RAM, two 16-bit timers and interrupt control for five interrupt sources.

2. Intel 8051
The 8051 is a second-generation Intel 8-bit microcontroller. The first Intel 8-bit microcontroller was the 8048.
Later, Intel introduced the 8049, which double the amount of ROM and RAM. Its architecture is the same as the 8048
A later introduction, the 8052, expands the size of ROM and RAM, but otherwise the architecture is the same as the 8051.

3. Intel 8051 An 8-bit ALU 4K x 8 ROM (or EPROM) 128 x RAM
Dual 16-bit timer event counter
32 I/O lines (4 I/O ports, 8-bit each)
Powerful 111-instruction set
Full-featured serial port
Up to 12-Mhz clock
Two external interrupts

4. Intel 8051
The 8051 can address external memory if there is not enough internal RAM and/or ROM. When used to address external memory, two ports provide the memory addressing.
The 8051 internal ROM is for program memory space. The program memory space is a read-only space. The processor cannot write data or read data from these memory locations.

5. Intel 8051
The RAM is the data memory space. It is a read-write memory space.
The processor can read data from this memory space and can write data to this memory space. It cannot execute program instructions from this memory space.
The 128 bytes of internal RAM (00H to 7FH) provide general read-write data storage. Part of this memory space is often referred to as general purpose registers.

6. Intel 8051
The 8051 also has 22 special-function registers occupy data memory space from 80H to F8H. Although addressable as memory locations, these registers must be used for their intended purpose.
If more program memory (ROM) is needed, the internal 4-Kbyte memory can be expanded by additional 60-Kbytes, giving the 8051 a full 64-kbytes program memory space. (see figure 9.1)

7. Intel 8051
If the 8051 EA pin is connected to ground, it does not use the internal 4K ROM. The external memory must start at memory location 0000H and can be up to a full 64kbytes. (8031 does not have internal ROM)

8. Figure 9.1

9. Figure 9.2

10. Intel 8051
If you need more RAM, you can add external data memory. You always have full use of all 64-kbytes of the external memory space. This memory is addressed separately from the internal 128 bytes of RAM.

11. Downloaded Program
Although the 8051 normally operates with separate program memory and data memory space, there are applications where 8051 can input a block of data through its serial communications port, load that data into memory, and then execute that data as a program. It is a very common technique used to change the program operating in a remote microprocessor-based controller.

12. Intel 8051 Internal RAM
The first 32 RAM locations are addressable as registers or as memory locations. By calling some memory locations registers, we can access them with single-byte instruction.
16 bytes of 8051 RAM are both bit and byte-addressable. The general instructions can address a byte of data at these memory locations. Other special instructions can address any individual bit in these memory locations. Bit instructions are very powerful tools when you need to process data words from external hardware devices.

13. Intel 8051 Internal RAM ..
Figure 9.2 is a memory map of the first 128 internal memory locations. The first 32 memory locations can be used as four register banks. There are eight registers in each bank. A register is an 8-bit read-write memory location which is addressed in a single-byte instruction. Because these single-byte instructions have only 3 bits available to address the register, they address only one of eight registers.

14. Special Function Registers
Special-function registers (SFRs). Each special-function register is dedicated to a single job.
The microprocessor’s SFRs are the accumulator (ACC E0H), the B register (B F0H), the program status word (PSW D0H), the stack pointer (SP 81H), the data pointer (DPTR) which is a 2 bytes register (DPL 82H and DPH 87H), and the power control register (PCON 87H).

15. Special Function Registers
Some of these SFRs are bit- and byte-addressable and others are only byte-addressable.
The accumulator is byte- or bit-addressable. It contains the operands or one of the operands of arithmetic or logical instruction and holds the result of that instruction.
The B register is used during multiply and divide operations as one 8-bit source and to hold the high-order 8 bits. It also can be as a simple scratch-pad register.

16. Special Function Registers
The program status word (PSW) is the 8051 status register. It is a bit-addressable register. 7 CY PSW.7 Carry flag 6 AC PSW.6 Auxiliary carry flag 5 F0 PSW.5 For general purpose use 4 RS1 PSW.4 Register bank selector bit 1 3 RS0 PSW.3 Register bank selector bit 0 2 OV PSW.2 Overflow bit 1 - PSW.1 Reserved 0 P PSW.0 Parity flag

17. Special Function Registers
Note that the 8051 PSW does not have zero bit.
Two special bits in the PSW (RS1 and RS0) indicate the current register bank. These bits can be set to select the current register bank or can be read to find out what register bank is selected
The 8051 stack pointer register is an 8-bit register, so it only addresses memory locations within the internal 128-bytes memory. It is incremental just before data is stored by using the push or call instruction, or the interrupt.

18. Data Pointer
The data pointer (DPTR) is a 16-bit register. It is made up of a High byte (DPH) and a Low byte (DPL). The data pointer holds a 16-bit address used when addressing external memory. The 8051 instructions let you work with the data pointer as a 16-bit register or as two separate 8-bit registers. If needed, a single- or double-byte instruction can operate on either the High or Low byte.

19. Power Control Register
Two bits of this register, PD (Power Down) and IDL (Idle), are only used in CMOS versions of the Bit 7 SMOD Double baud rate bit Bit 3 GF1 General purpose flag bit Bit 2 GF0 General purpose flag bit Bit 1 PD Power down bit Bit 0 IDL Idle mode bit

20. Counter-Timer Control Register
TCON is used to control the function of counter-timer. TF1 TCON.7 Timer 1 overflow flag TR1 TCON.6 Timer 1 run control bit TF0 TCON.5 Timer 0 overflow flag TR0 TCON.4 Timer 0 run control bit IE1 TCON.3 External interrupt 1 flag IT1 TCON.2 Interrupt 1 type control IE0 TCON.1 External interrupt 0 flag IT0 TCON.0 Interrupt 0 type control

21. Counter-Timer Mode Control Register
It is used to set the mode of counter-timers. Bit 7 (Timer 1) Gate, when TR1 of TCON is set and Gate=1, Timer1 will run only while INT1 pin is high. Bit 6 (Timer 1), C/T, timer or counter selector Bit 5 (Timer 1) M1, Mode selector bit 1
Bit 4 (Timer 1) M0, Mode selector bit 0

22. 8051 Interrupt System
There are five different ways to interrupt an Two of these are from external electrical signals. The other three are caused by internal 8051 I/O hardware operations.
The two external inputs come from the INT0 and INT1 inputs. A logic 0 on INT0 sets bit IE0 (interrupt external 0) in the timer control register. A logic 0 on INT1 sets bit IE1

23. Intel 8051

25. Intel 8051
Port 0 is at address 80H, port 1 at address 90H, port 2 at address A0H and port 3 at address B0H. When a port is to be used as an output port the data is put into the corresponding special register. When a port is to be used as an input port, the value FFH must first be written to it.

26. Intel 8051 RXD is the serial input port TXD is the serial output port
INT0 is the external interrupt 0
INT1 is the external interrupt 1
T0 is the timer/counter 0 external input
T1 is the timer/counter 1 external input
WR is the external memory write strobe
RD is the external memory read strobe

27. Intel 8051
The term strobe describes a connection used to enable or disable a particular function.
ALE
The address latch enable pin provides an output pulse for latching the low-order byte of the address during access to external memory. This allows 16-bit addresses to be used. (see next slide)

28. Use of ALE

29. Intel 8051
PSEN
The program store enable pin is the read signal pin for external program memory and is active when low. It is connected to the output enable pin of external ROM or EPROM. EA
The external access pin is taken low for the microprocessor to access only external program code; when high it automatically accesses internal or external code, depending on the address. This pin also used on a microcontroller with EPROM to receive the programming supply voltage for programming the EPROM

30. Intel 8051
XTAL1, XTAL2
These are the connecting pins for a crystal or external oscillator.
RESET A high signal for a minimum of two machine cycles on this pin resets the microcontroller.

31. Intel 8051 Serial input/output
Writing to the serial data buffer SBUF at address 99H load data for transmission; reading SBUF accesses received data.
Timing The timer mode register TMOD at address 89H is used to set the operating mode for timer 0 and timer 1. The timer control register TCON contains status and control bit for timer 0 and timer 1.

32. Intel 8051
Interrupts
Interrupts force program to call a subroutine located at a specified address in memory; they are enable by writing to the interrupt enable register IE at address A8H.
Bit 7 = EA (Global Enable/Disable) Bit 4 = ES (Enable serial port interrupt) Bit 3 = ET1 (Enable Timer 1 interrupt)
Bit 2 = EX1 (Enable external 1 interrupt) Bit 1 = ET0 (Enable timer 0 interrupt) Bit 0 = EX0 (Enable external 0 interrupt)