ZiLOG Z8S18000ZEM User Manual page 29

Z
ILOG
Before the Monitor executes the user program, it proceeds as follows:
1. Checks to see if the opcode at the starting address is a hard-coded RST 28H. If so, it advances
the starting address over the RST 28H and proceeds to Step 3.
2. If not, it checks for a breakpoint at the starting address. If so, it invokes an implicit T command,
to single step over the first instruction, returning to Step 3 when this has been completed.
3. For each breakpoint, it saves the opcode at that address in a RAM table and substitutes the
opcode RST 28H (EF).
4. It stacks the starting address and restores all the user register values that were saved in the last
RESET, breakpoint, hard-coded RST 28, or NMI, and may have modified since then.
5. It enables or disables interrupts per the saved EI value.
6. It uses a RET instruction to begin execution at the starting address stacked in Step 4.
After a G command, there are several ways that control can return to the Monitor:
If execution comes to an RST 28 instruction, either a breakpoint or hard-coded one
If execution comes to an illegal instruction
Or when you press the NMI or RESET push button
In all of these cases except RESET, the Monitor saves the program counter. In all cases, it saves the
register contents, and restores the opcodes of any set breakpoints. Then, for NMI or an illegal
instruction, it displays a message why execution stopped, and in any case displays the register
contents, program counter, and the instruction in hexadecimal and disassembled formats.
Example:
Z80180>
File name: jonestst
78 Intel hex lines - Done
Z80180>Go starting at Address :
Z80180 ASCI Tx hacking: v.1.0
Please set jumpers as follows:
ASCI0 RXA to ESCC TXD
ASCI0 TXA to ESCC RXD
ASCI0 /DCD to PIA12
ASCI0 /CTS to ESCC /RTS
ASCI0 /RTS to ESCC /CTS
Press 'G' on keyboard when ready...
ST951800100
(Eval bd. J12-3 to J10-2)
(Eval bd. J12-2 to J10-3)
(Eval bd. J12-8 to J12-20
and J14-12 to J14-13)
(Eval bd. J12-5 to J10-4)
(Eval bd. J12-4 to J10-5)
UM010501-0301
Z8S180 E
MULATOR
U ' M
SER S ANUAL
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