Z89C6501ZEM Datasheet, PDF (4/6 Pages) Zilog, Inc. – ICEBOX FAMILY Z8 IN-CIRCUIT EMULATOR -C65

LIMITATIONS (Continued)
Z89C65/165 ROM Emulation
The Z89C65/165 ROM emulation has the correct
sequence for vectored interrupts, shown as follows:
Push Program Counter (PC) lower byte on stack
Push PC upper byte on stack
Push FLAG on stack
Fetch the upper byte of vector
Fetch the lower byte of vector
Branch to service routine specified by vector
Z89C6501ZEM
CP96TAD00403
Z89C66/166 ROMless Emulation
The Z89C66/166 ROMless emulation has the incorrect
sequence for vectored interrupts. This sequence is shown
as follows:
Push PC lower byte on stack
Push PC upper byte on stack
Push FLAG on stack
Fetch the upper byte of vector
Write the upper byte of vector to high byte of PC
Fetch lower byte of vector according to the modified
PC
Branch to service routine specified by vector
The following figures illustrate the vectored interrupt
operation for ROM and ROMless emulation, respectively.
0153
000C
Correct Interrupt
Service Routine
0178
78
0103
000C
Incorrect Interrupt
Service Routine
0003
53
0002
01
IRQ1
Vector
0003
53
0002
01
IRQ1
Vector
0000
0000
Z8 Program Memory
Z89C65/165 ROM Emulation
Z8 Program Memory
Z89C66/166 ROMless Emulation
Note: The Incorrect Vectored Interrupt emulation only applies to the emulator.
The Z89C66/166 device does not exhibit this problem.
Vectored Interrupt Operation for ROM and ROMless Emulation
4