3. Functional blocks
• Registers
• ALU
• Instruction decoder and machine cycle encoder
• Address buffer
• Address / Data buffer
• Incrementer / Decrementer Address Latch
• Interrupt control
• Serial I/O control
• Timing and control circuitry
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4. 1.Registers
• General purpose registers
• Temporary registers
• Special purpose registers
• Sixteen bit registers
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5. General purpose registers
• B,C,D,E,H,L are 8 bit registers.
• Combination of BC,DE,HL registers are form a 16 bit
registers
• HL pair also function as a data pointer or memory pointer
• To store intermediate results in their memory
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6. Temporary registers
• Temporary storage registers to store one input
for arithmetic and logical operations
• Programmer cannot access this registers
externally
• W and Z registers are used as temp. registers.
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7. Special purpose registers
• Accumulator – tri-state 8 bit register, used in
arithmetic logical operations and mostly the
performed results are stored in it.
• Flag Register-8 bit registers.
Sign Flag- D7-1 the num is negative
D7-0 the num is positive
Zero Flag- set if ALU result is zero
Reset if ALU result is non-zero
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8. • Auxiliary carry flag
flag is set if the bit is overflow out of bit 3.
Parity flag
-the number of 1’s present in accumulator,
-Even parity means flag set
-Odd Parity means flag reset
Carry Flag
-flag is set if there is an overflow of bit 7.
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9. 16-bit registers
• Program counter (PC)
-stores the address of next instruction to be
fetched.
-PC acts as a pointer to the next instruction.
• Stack pointer (SP)
- to hold the address of the most recent stack
entry.
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11. Instruction decoder
• Fetch and store the opcode in instruction
register.
• Decodes the opcode and gives timing and
control signals which control reg.,data
buffers,ALU,external peripherals.
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12. Address buffer
• 8-bit unidirectional buffer
• Tri-state high order address bus under such
conditions like halt,hold , reset.
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13. Address /data buffer
• 8-bit unidirectional buffer
• Low order address bus and data bus
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14. Incrementer /Decrementer latch
• 16-bit register
• Used to INC / DEC. the contents of program
counter and stack pointer
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15. Interrupt control
• Sometimes there will be need to make a
interrupt to allow or block the signals for
some time.
• RST5.5,RST 6.5,RST7.5 ,TRAP,INTR AND INTA.
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16. Serial I/O control
• SID-Serial input data for receive data.
• SOD-Serial output data for sending data.
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17. Timing and control
• For fetching and decoding operations and
generating appropriate signals for instruction
execution ,control circuitry.
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