167μPD1706213.6 OPERATION OF THE DEVICE AT A HALT OR CLOCK STOP13.6.1 State of Each Pin at a Halt and Clock StopTable 13-1 summarizes how the CPU and peripheral hardware behave during the halt or clock stop state.During the halt state, execution of the CPU instructions is suspended, but the peripheral hardware operatesnormally, as described in Table 13-1.During the clock stop state, on the other hand, all peripheral hardware is at a stop.During the halt state, the control register that controls the operating state of the peripheral hardware worksas usual (not initialized). During the clock stop state (when the STOP s instruction is executed), on the otherhand, the control register is initialized to a specified value.To put in another way, the peripheral hardware keeps operating as specified in the control register duringthe halt state. During the clock stop state, however, the peripheral hardware operates according to the initialvalue set in the control register.See Chapter 9 for the initial value for the control register.Let’s study the following example.Example When the P0A 0 /SDA and P0A 1 /SCL pins of port 0A are specified as output ports, and the P0A2 /SCK and P0A 3 /SO pins are used as a serial interfaceHLTINT DAT 1000B ; Defines a symbol.XTAL DAT 0000B ;INITFLG P0ABIO3, P0ABIO2, P0ABIO1, P0ABIO0; Built-in macro; #SET2 P0A0, P0A1 ;INITFLG SIO0CH, NOT SB, SIO0MS, SIO0TX;SET2 SIO0CK1, SIO0CK0; $SET2 SIO0IMD1, SIO0IMD0CLR1 IRQSIO0SET1 IPSIO0EI; %SET1 SIO0NWT; &HALT HLTINT; (STOP XTALThe above program outputs a high level from the P0A 0 and P0A 1 pins at #, specifies a serial interfacecondition at $, and starts serial communication at %.When the HALT instruction is executed at &, the serial communication continues, and the halt state isreleased after a serial interface interrupt request is accepted.
