Debug: R--Notes

Using the R command

If you specify a register name, Windows NT displays the 16-bit value of that register in hexadecimal notation and displays a colon as the prompt. If you want to change the value contained in the register, type a new value and press ENTER; otherwise, just press ENTER to return to the Debug prompt.

Valid register names

The following are valid values for register-name: ax, bx, cx, dx, sp, bp, si, di, ds, es, ss, cs, ip, pc, and f. Both ip and pc refer to the instruction pointer.

If you specify a register name other than one from the preceding list, Windows NT displays the following message:

br error

Using the f character instead of a register name

If you type the f character instead of a register name, Debug displays the current setting of each flag as a two-letter code and then displays the Debug prompt. To change the setting of a flag, type the appropriate two-letter code from the following table:

Flag name	Set	Clear
Overflow	ov	nv
Direction	dn (decrement)	up (increment)
Interrupt	ei (enabled)	di (disabled)
Sign	ng (negative)	pl (positive)
Zero	zr	nz
Auxiliary Carry	ac	na
Parity	pe (even)	po (odd)
Carry	cy	nc

You can type new flag values in any order. You need not leave spaces between these values. To stop the r command, press ENTER. Any flags for which you did not specify new values remain unchanged.

Messages displayed with the r command

If you specify more than one value for a flag, Debug displays the following message:

df error

If you specify a flag code not listed in the preceding table, Debug displays the following message:

bf error

In both cases, Debug ignores all settings specified after the invalid entry.

Default settings for Debug

When you start Debug, the segment registers are set to the bottom of free memory, the instruction pointer is set to 0100h, all flags are cleared, and the remaining registers are set to zero, except for sp, which is set to FFEEh.

More Information About Debug: R

Debug: R--Examples

Debug: R