mitsubishi - Al Kossow's Bitsavers

MITSUBISHI MICROCOMPUTERSMSM82C43PINPUT/OUTPUT EXPANDERPIN DESCRIPTIONSymbol Name Input or output Function-C$ Chip selectInChip select input. A high on CS causes PROG input to be regarded high inside the M5M82C43P. Thisthen inhibits any change of output or internal status.A high-to-Iow transition on PROG signifies that address (ports 4-7) and' control are available on port 2,PROG Program In and a low-to-high transition signifies that the designated data is available on the designated port throughport 2. The designation is shown in Table 1.P2 0 ...... P2 3 Input/output port 2 In/outThis 4-bldlrectional port contains the address and control bits shown in Table 1 on a high-to-Iow transitionof PROG. During a low-to-high tranSitiOn, it contains the input (output) data on this port.P4 o ...... P4 3 Input/output port 4 4-bit bidirectional I/O ports. May be programmed to be input, low-Impedance latched or 3-state. TheseP5 0 ...... P5 3 Input/output port 5ports are automatically set to the output mode when written, ANLed or ORLed and this mode continuesIn/outP6 0 ...... P6 3 Input/output port 6 until the next read operation. After reset on a read operation, this port Is placed in the high ImpedanceP7 o ...... P7 3 Input/output port 7 and input mode.OPERATIONThe M5MB2C43P is an input/output expander designedspecifically for the MELPSB-41 and MELPSB-4B. TheMELPS8-41 and MELPS8-4B already have instructions andPROG pin to communicate with the M5M82C43P.An example of the M5M82C43P and the M5MBOC49-XXXP isshown in Fig. 1. The following description of theM5M82C43Pbasic operation is made according to Fig. 1.Upon initial application of the power supply to the device,each port of the M5MB2C43P is set to the input mode (highimpedance)by means of the resident power-on initializationcircuit.When the microcomputer begins to execute a transfer instructionMOVO A, Pi i = 4,5,6.7which means the value on the port Pi is transfer~d to theaccumulator. then the signals are sent out on the pinsPROG and P2o ...... P2 3 • as shown in the timing diagram.On the high-to-Iow transition of pin PROG. the M5M82C43Platches the instructions (e.g. 0000) into itself from pins P2o ......P2 3 and transfers them to the instruction register (CD in thetiming diagram). During the low-level of PROG, theM5M82C43P continuously outputs the contents of the specifiedinput (output) port (in this case, port P4) to pins P2o ......P2 3 (~ in the timing diagram). The microcomputer. at theappropriate time. latches the level of pins P2o ...... P2 3 and resumesthe, high level of PROG.The next example is the case in which the microcomputerexecutesMOVO PI, A i = 4. 5. 6. 7the transfer (output) instruction.In this case. as in the previous case, on the high-to-Iowtransition of pin PROG. the M5MB2C43P latches the instructions(e.g.Oll0) into itself from pins P2o ...... P2 3 and transfersthem to the instruction register (CD in the timing diagram).After this the microcomputer sends out high to pin PROG.transferring the data to pins P2o ...... P2 3 which is an outputdata to the input/output port. Then the M5MB2C43P transfersthe data of pins P2o ...... P2 3 to the port latch of the designatedinput/output port (in this case P6). In a few secondsafter a low-to-high transition on the PROG. the designatedport (P6) is set to the output mode and the data of the portlatch is transferred to the port pins (@ in the timingdiagram).When instructionsANlOORlOPi,APi,A i = 4.5.6.7are executed. the microcomputer generally operates as thesame function as MOVD Pi.A.It only differs in that the data of the port latch after ® in thetiming diagram is ANDed or ORed with the data of the portlatch before ® and the data of pins P2o ...... P2 3 .When instructionsMOVO Pi, AANlO Pi,AORlO Pi,A i = 4. 5, 6. 7are executed toward the· port in an output mode, the outputsare generated on the port as soon as low-to-high transitionon the PROG occurs.When the mode of the output port is going to be changedduring the execution and the instructionMOVO A,Pi i=4.5.6.7is executed. it is preferable to execute one dummy instruction'.Because it takes a little time to turn the designatedport into a high-impedance state after the high-to-Iow transitionon the PROG, the result may be that the first instructionis not read correctly .II•• . MITSUBISHI.... ELECTRIC6-33