M16C User Manual.pdf

Bus ControlMitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTER(6) Hold signalThe hold signal is used to transfer the bus privileges from the CPU to the external circuits. Inputting “L” to__________the HOLD pin places the microcomputer in the hold state at the end of the current bus access. This status____________________is maintained and “L” is output from the HLDA pin as long as “L” is input to the HOLD pin. Table 1.12.6shows the microcomputer status in the hold state.__________Bus-using priorities are given to HOLD, DMAC, and CPU in order of decreasing precedence.Figure 1.12.4. Bus-using prioritiesTable 1.12.6. Microcomputer status in hold stateItem__________HOLD > DMAC > CPUStatusOscillationON___ _____ _______R/W signal, address bus, data bus, CS, BHEFloatingProgrammable I/O ports P0, P1, P2, P3, P4, P5 FloatingP6, P7, P8, P9, P10 Maintains status when hold signal is received__________HLDAOutput “L”Internal peripheral circuitsON (but watchdog timer stops)ALE signalUndefined(7) External bus status when the internal area is accessedTable 1.12.7 shows the external bus status when the internal area is accessed.Table 1.12.7. External bus status when the internal area is accessedItem SFR accessed Internal ROM/RAM accessedAddress bus Address output Maintain status before accessedaddress of external areaData bus When read Floating FloatingWhen write Output data UndefinedRD, WR, WRL, WRH RD, WR, WRL, WRH output Output "H"BHE BHE output Maintain status before accessedstatus of external areaCS Output "H" Output "H"ALE Output "L" Output "L"38