Zilog Z80195 - Manual (Page 32)

Z80185/195 D EVELOPMENT K IT
U SER ' S M ANUAL
3-12 UM951800100
Z ILOG
Display/Alter Registers [R]
You will be asked for a starting register. If no register name is supplied, all CPU registers are
displayed. If a register name is supplied, display starts from that register, and the values can be
modified.
<ESC> Does not store a preceding value and returns to the command prompt.
. Stores a preceding value if any and returns to the command prompt.
= Stores a preceding value if any, stays at the same location, re-reads and re-
displays.
CR,tab,Space,+,> Stores a preceding value if any, and go to the next location.
-,<,^ Stores a preceding value if any, and go to previous location.
Example:
Z80185 > Display/Alter Register (just CR Displays All) :
A F B C D E H L A’ F’ B’ C ’ D’ E’ H’ L’ I IX IY SP EI
02 00 0F 04 00 00 20 A7 FE 80 00 00 00 00 00 00 00 021B 0000 205E 0
OFDD CB7F BIT 7,A
Step (Over Subrouting Calls) [S]
This command steps a specified number of instructions, stepping “over” subroutine calls and RST.
In this command, monitor stores an EF opcode after the instruction, so that it will get control back after
the subroutine has complete execution and returns.
If no value is entered, then “1” step is assumed. If the user enters more than two hex digits, only the
LS 2 hex digits are used, so the maximum number of instructions that can be step by one command
is 255 (decimal). For each instruction step over, the monitor will display the register values, the
Program Counter, and the instruction in both hex and disassembled format. The instructions to be
stepped over must be in RAM. The monitor accomplishes stepping by placing the opcode (EF) RST
28H after each instruction, and/or for instruction, by placing the EF opcode at the destination. It then
restores the registers and transfers control to the single instruction, being assured of getting control
right back because of the RST 20s. Simple operations (such as unconditional JR, JP, and RET) are
handled by updating the user PC without storing any RST 28s. RST instructions can only be “stepped
over” with an “S” command, because they transfer the control into ROM. A hard-coded RST 28 is
treated as a No-Op while stepping. The monitor advances the program counter to the next instruction.
The RST 28s are not placed at breakpoints while stepping.
Example:
Z80185 > Step How Many Instructions: