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    Register command

    Purpose:  The Register command has three functions:

              .   It displays the hexadecimal contents of a single regi-
                  ster, with the option of changing those contents.

              .   It displays the hexadecimal contents of all the regi-
                  sters, plus the alphabetic flag settings, and the next
                  instruction to be executed.

              .   It displays the eight 2-letter alphabetic flag settings,
                  with the option of changing any or all of them.

    Format:   R [registername]

    Remarks:  When the DEBUG program starts, the registers and flags are
              set to certain values for the program being debugged (see
              Starting DEBUG).

              Display a single register                                   

              The valid registernames are:

              AX        BP        SS
              BX        SI        CS
              CX        DI        IP
              DX        DS        PC
              SP        ES        F

              Both IP and PC (program counter) refer to the instruction
              pointer.

              For example, to display the contents of a single register,
              you might enter:

              R AX

              The system might respond with:

              AX F1E4
              :_

              Now you may take one of two actions:

              .   Press Enter to leave the contents unchanged.
                  or
              .   Change the contents of the AX register by entering a
                  1-4 character hexadecimal value, such as 0FFFh.

              AX F1E4
              :FFF_

              Now pressing Enter changes the contents of the AX register
              to 0FFFh.


              Display all registers and flags                             

              To display the contents of all registers and flags (and the
              next instruction to be executed), type:

              R

              The system might respond with:

    AX=0E00  BX=00FF  CX=0007  DX=01FF  SP=039D  BP=0000  SI=005C  DI=0000
    DS=04BA  ES=04BA  SS=04BA  CS=04BA  IP=011A   NV UP DI NG NZ AC PE NC
    04BA:011A   CD21          INT     21

              The first two lines display the hex contents of the registers
              and the eight alphabetic flag settings. The last line indi-
              cates the location of the next instruction to be executed,
              and its hex and unassembled formats. This is the instruction
              pointed to by CS:IP.


              Display all flags                                           

              There are eight flags, each with 2-letter codes to indicate
              either a set or clear condition.

              The flags appear in displays in the same order as presented
              in the following table:


              Flag Name                            Set   Clear
              Overflow (yes/no)                    OV    NV
              Direction (decrement/increment)      DN    UP    (DowN/UP)
              Interrupt (enable/disable)           EI    DI
              Sign (negative/positive)             NG    PL    (NeG/PLus)
              Zero (yes/no)                        ZR    NZ
              Auxiliary carry (yes/no)             AC    NA
              Parity (even/odd)                    PE    PO
              Carry (yes/no)                       CY    NC


              To display all flags, enter:

              R F

              If all the flags are in a set condition, the response is:

              OV DN EI NG ZR AC PE CY -_

              Now you can take one of two actions:

              1.  Press Enter to leave the settings unchanged.
              2.  Change any or all of the settings.

              To change a flag, just enter its opposite code. The opposite
              codes can be entered in any order - with or without interven-
              ing spaces. For example, to change the first, third, fifth,
              and seventh flags, enter:

              OV DN EI NG ZR AC PE CY - PONZDINV

              They are entered in reverse order in this example.

              Press Enter and the flags are modified as specified, the
              prompt appears, and you can enter the next command.

              If you want to see if the new codes are in effect, enter:

              R F

              The response is:

              NV DN DI NG NZ AC PO CY -_

              The first, third, fifth, and seventh flags are changed as
              requested. The second, fourth, sixth, and eighth flags are
              unchanged.

              Note:
              A single flag can be changed only once per R F command.