mitsubishi - Al Kossow's Bitsavers

MITSUBISHI MICROCOMPUTERSMELPS 8-48 MICROCOMPUTERSFUNCTION OF MELPS 8-48 MICROCOMPUTERSThe STRT T instruction is used to change the counterto a timer. The internal clock signal becomes the input tothe timer. The internal clock is 1/32 of 400kHz (whenusing 6M Hz crystal) or 12.5kHz. The timer is thereforecounted up every 80ps. Fig. 9 shows the timer/eventcounter.The counter can be initialized by executing an MOV T,A instruction. The timer can be used to measure 80ps'"20ms in multiples of 80ps. When it is necessary to measureover 20ms (maximum count 256x80ps) of delay time thenumber of overflows,one every 20ms, can be counted bythe program. To measure times of less than 80ps; externalclock pulses can be input through T 1 while the counter isin the event counter mode. Every third (or more) ALE signalcan be used instead of an external clock.I, irONDI:ONAjJUMPMELPS 8-48 CYCLE TIMINGThe output of the state counter is 1/3 the input frequencyfrom the oscillator. When a 6MHz crystal is used for input,the output would be 2MHz (500ns). A eLK signal is generatedevery 500ns (one state cycle) which is used for thedemarcation of each machine state. The instruction ENTOeLK will output the elK signal through terminal To. Theinput of the cycle counter is eLK (state cycle) and the outputis an ALE signal which is generated every 5 statecycles.Fig. 11 Shows the relationship between clock and generatedcycles.One machine cycle contains 5 states with a eLK signalfor demarcation of each state. The MELPS 8-48 instructions.are executed in one machine cycle or two machine cycles.An instruction cycle can be one or two machine cyclesas shown in Fig.12.IIT1I JTFI TI~ERIOVERFLOW,FLAGINTERRUPT ENABLEINTERRUPTREQUESTFig. 9 Timer/event counterFig.10 Clocking cycle generation_I~ClK(OUTPUT TO To)500ns(WHEN USING A 6MHz CRYSTAL)52 53 54 55 51 52 53 54 55~~WL~~,...I1..J"1.~~~ALEr-h r-II.P5ENRDWR ~PROGIFlg.11 Clock and generated cycle sIgnalsINSTRUCTION EXECUTION2 MACH I NE CYCLES 1--+--+-___5o --'i)l_s____-iFig.12 Instruction execution timing• MITSUBISHI"ELECTRIC4-11