Intel 8086-1, 8086-2 manual BUS TIMING-MEDIUM Size Systems

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lines D7 – D0 as supplied by the inerrupt system logic (i.e., 8259A Priority Interrupt Controller). This byte identifies the source (type) of the interrupt. It is multi- plied by four and used as a pointer into an interrupt vector lookup table, as described earlier.

BUS TIMING—MEDIUM SIZE SYSTEMS

For medium size systems the MN/MX pin is con- nected to VSS and the 8288 Bus Controller is added to the system as well as a latch for latching the sys- tem address, and a transceiver to allow for bus load- ing greater than the 8086 is capable of handling. Signals ALE, DEN, and DT/R are generated by the 8288 instead of the processor in this configuration although their timing remains relatively the same. The 8086 status outputs (S2, S1, and S0) provide type-of-cycle information and become 8288 inputs. This bus cycle information specifies read (code, data, or I/O), write (data or I/O), interrupt

8086

acknowledge, or software halt. The 8288 thus issues control signals specifying memory read or write, I/O read or write, or interrupt acknowledge. The 8288 provides two types of write strobes, normal and ad- vanced, to be applied as required. The normal write strobes have data valid at the leading edge of write. The advanced write strobes have the same timing as read strobes, and hence data isn’t valid at the leading edge of write. The transceiver receives the usual DIR and G inputs from the 8288’s DT/R and DEN.

The pointer into the interrupt vector table, which is passed during the second INTA cycle, can derive from an 8259A located on either the local bus or the system bus. If the master 8259A Priority Interrupt Controller is positioned on the local bus, a TTL gate is required to disable the transceiver when reading from the master 8259A during the interrupt acknowl- edge sequence and software ‘‘poll’’.

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Contents CPU Block Diagram Pin ConfigurationBHE LOW BHE/SReady ResetIntr TestHigh LOWRQ/GT0 RQ/GT1ALE IntaDT/R DENFunctional Description BUS Operation Minimum and Maximum ModesMinimum Mode 8086 Typical Configuration Write I/O Read I/OInstruction Fetch Read Data from MemoryAlternate Data extra segment Processor Reset and InitializationAddressing Interrupt OperationsHalt Maskable Interrupt IntrREAD/MODIFY/WRITE Semaphore Operations VIA Lock System TIMING-MINIMUM System External Synchronization VIA TestBUS TIMING-MEDIUM Size Systems Absolute Maximum Ratings Tclcl Minimum Complexity System Timing RequirementsTclch TchclTiming Responses CharacteristicsMinimum Mode Testing INPUT, Output Waveform Testing Load CircuitWaveforms Waveforms Minimum Mode Tinvch CharacteristicsNMI, Test Tgvch TchgxTclmh TclmlTryhsh TchsvTCLCL-45 TCLCL-35 TCLCL-40 TrhavTchdtl TchdthMaximum Mode Waveforms Maximum Mode BUS Lock Signal Timing Maximum Mode Only Reset Timing Asynchronous Signal RecognitionREQUEST/GRANT Sequence Timing Maximum Mode only WaveformsHOLD/HOLD Acknowledge Timing Minimum Mode only Data Transfer Instruction Set SummaryArithmetic Logic 8086 1 reg 1 1 Data Sheet Revision ReviewBit w e Segment 000 001 010 011 100 101 110 111
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