section 7 - Index of

PROGRAM CONTROL UNIT-23 1615 023 1615 0I '---'-LO-O-P-A-DD---R-ES-S---' * I " LOOP * I COUNTER (LC) IREGISTER (LA)231615 0231615 87 0I * I II * I MA I eCA IPROGRAMCOUNTER (PC)STATUSREGISTER (SR)31 SSH 1615 SSL23 8 7 6 5 4 3 2 1 0I * 1* Isol*IMClvoloEIMSIMAIOPERATING MODE REGISTER (OMR)23 6 5 0~---~I _*~I~~==~ __ ~ISTACK POINTER (SP)SYSTEM STACK1* READ AS ZERO, SHOULD BE WRITTENWITH ZERO FOR FUTURE COMPATIBILITYFigure 5-4 Program Control Unit Programming Modelation, move the contents in accumulator A into the location in Y data memory pointed toby R4 and postdecrement R4. The third instruction, 13, is the same as 11, except therounding operation is not performed.5.4 PROGRAMMING MODELThe program control unit features LA and LC registers which support the DO loop instructionand the standard program flow-control resources, such as a PC, complete SR, andSS. With the exception of the PC, all registers are read/write to facilitate system debugging.Figure 5-4 shows the program control unit programming model with the six registersand SS. The following paragraphs give a detailed description of each register.5.4.1 Program CounterThis 16-bit register contains the address of the next location to be fetched from programmemory space. The PC can point to instructions, data operands, or addresses of operands.References to this register are always inherent and are implied by most instructions.