HP 271308 Technical Reference Manual

HP 27130BSIGNAL NAMEAO - A15(Address Bus)DO - D7(Data Bus)M1-(Machine Cycle 1)MREQ-(Memory Request)IORQ-(Input/Output·Request)Table 3-4. Z-80B CPU SignalsFUNCTIONTri-state output, active high.AO - A15 are a 16-bit address bus (AO is theleast significant bit). This bus providesaddress capability for up to 64K of memory dataexchanges, and for I/O device data exchanges.I/O addressing uses the 8 lower address bitsto allow direct addressing of up to 256 inputor 256 output ports.Tri-state input/output, active high.DO - D7 are an 8-bit bidirectional data busused for data exchanges with memory and I/Odevices.Output, active low.Indicates that the current machine cycle isthe OP code fetch cycle of an instructionexecution.Tri-state output, active low.Indicates that the address bus holds a validaddress for a memory read or write.Tri-state output, active low.Indicates that the lower half of the addressbus holds a valid I/O address for an I/O reador write. 10RQ- is also generated with M1-when an interrupt is being acknowledged.Interrupt acknowledge operations occur duringM1 time, while I/O operations never occurduring M1 time.3-10