Digital Electronics: Principles, Devices and Applications

{{546 Digital ElectronicsSystem Data BusHalt StateMemory RequestInput/Output RequestReadWriteBus AcknowledgeMachine Cycle 1RefreshInterrupt RequestNon-Maskable InterruptWaitBus Request181920212223272816172425CPU Timing ControlInstructionDecoderInstructionRegister13 10 9 7 8 12 15 14Data Bus InterfaceRegister ArrayALUReset26Address Bus Interface11 29 6V cc GND System(+5V) (0V) Clock5 4 3 2 1 40 39 38 37 36 35 34 33 32 31 30System Address BusFigure 13.14Block diagram of Z-80.OR, EXCLUSIVE-OR, complement and shift/rotate), control transfer (conditional, unconditional, callsubroutine and return from subroutine) and others – clear/set condition flags, bit test, stack operations,software interrupt, etc.13.9.3 Zilog Z80 MicroprocessorThe Zilog Z80 microprocessor is an eight-bit processor that is object-code compatible with Intel 8080.It is available in industry-standard 40-pin dual in-line and 44-pin chip carrier packages. The maximumoperating frequency is 2.5 MHz. Figure 13.14 shows a block diagram of Z80.13.9.3.1 Z80 registersThe Z80 microprocessor has registers compatible with the 8080 microprocessor as well as some otherregisters. The 8080-compatible registers include the accumulator, flag register (F), general-purposeregisters (six programmable general-purpose registers designated B, C, D, E, H and L), stack pointer(SP) and program counter. The registers introduced with Z80 are the alternate accumulator register(A ′ ), the alternate flag register (F ′ , the alternate B, C, D, E, H and L registers (represented as A ′ ,B ′ ,C ′ ,D ′ ,E ′ ,H ′ and L ′ ), the index registers (IX and IY), the interrupt vector register (I) and the memoryrefresh register (R).13.9.3.2 Instruction setThe Z80 microprocessor has 158 instructions. They perform data copy (transfer) or load operations,arithmetic, logic operations, bit manipulation, branch operations and machine control operations.