mitsubishi - Al Kossow's Bitsavers

MITSUBISHI MICROCOMPUTERSMS0740-XXXS PSINGLE.CHIP a·BIT CMOS MICROCOMPUTERReset CircuitWhen a supply voltage of 5V ±10% is being supplied to the.M50740-XXXSP and the RESET pin is returned to the highlevel after being kept at the low level for 2J1s or more, thereset is released in accordance with the sequence shownin Fig. 6, and the program starts from the address which isderived from the contents of the address 1 FFF 16 and 1 FFE 16,high-order address is the contents of address 1 FFF 16 andlow-order address is the contents of address 1 FFE 16 . Whenresetting is accomplished, the internal state of the microcomputeris as shown in Fig. 7.Fig. 8 shows an example of the reset circuit.The reset input voltage should be set to less than 0.6V atthat point when the supply voltage is passing through 4.5V.Address(1) Data direction ( E 1 16 )···1 o 0 16Iregister of port 0(2) Data direction ( E ~ 16 ) ... [ o 0 16Iregister of port 1) ···1 [(3) Data direction ( E 5 16 o 0 16register of port 2(4) Data direction ( E 9 16 ) .. ·1 o 0 16Iregister of port 3(5) Prescaler X ( F C 16) ... F F 16IPower onM50740~XXXSPOVM50740-XXXSPRESETVee'::2'::T 2 -----e52~ Supply voltager- ---.:..--~ detection circuitIIIIIIII~----~~ II, IIIIIIIIIL ________ JFig.8 Example of reset circuitII(6) Timer X ( F D 16) ... o 1 161(7) Interrupt control register ( FE 16 ) ...o 0 16 1(8) Timer control register ( F F 16 ) ... o 0 16I(9) Interrupt disable flag ( PS ) ...[on the processor statusregister1 1[ [1[ [I00) Program counter ( PC H(11) The oscillator output isconnected to pin X OUTF aswith the state establishedafter the FST instructionhas been executed.Fig.7) ... 1 contents of the ,Iaddress 1 FFF 16( P C L) .1 contents of th.e ; 1... address 1 FFE 16Internal state of microcomputer after resettingInput/Output Pins(1) Port POThis port is an 8-bit input/output port with n-channelopen-drain outputs. As shown in the memory map ofFig. 1, port PO is treated as the memory of address E0 16on the zero page. Port PO has a data direction register(address El l6 on zero page) and programming can beundertaken for individual bit to use the port for input oroutput. The pins where the data direction register isprogrammed to "1" are for output and those where theregister is programmed to "0" are for input. The datawritten into the pin programmed as an output pin arewritten into the port latch and supplied direct to theoutput pin. When reading. the. data from a pin programmedas an output pin! it is not the output pin contentswhich are read but the port latch contents. Consequently,since the LED or other similar part is drivendirectly, the value output previously can be read correctlyeven if the low-level output voltage rises. Thepin programmed as an input pin remains floating, soexternal signal can be read. When data are written,they are written into the port latch only and the pin remainsfloating.• MITSUBISHI.... ELECTRIC3-11