EMS6500 EM Microelectronic, EMS6500 Datasheet - Page 42

• Manufacturer Part Number: EMS6500
• Description: Microcontroller Development System 4-bit (Emmon), Simulators 4-bit
• Manufacturer: EM Microelectronic

EM66xx
Development System
instruction which returns to the address following the a CALL instruction) and resets
the INT flag.
If interrupts are enabled then the programmer should be careful to only use two
program counters in the main body of the program, since one should be reserved for
the interrupt handler call. The interrupt handler routine must be placed at the
address 001H and should be terminated with a RTI instruction. On entering the
interrupt handler the Cy_int flag is automatically selected. However, the value of the
Accu should be saved to a temporary RAM location. The value of Accu should also
be restored prior to the execution of the RTI instruction. For an overview of the
advised program structure please see fig. 2.
The EM66xx micro controllers only have one interrupt handler and cannot perform
nested interrupts. If a second interrupt signal arrives when the controller is already
interrupted then the signal is not processed until the controller has finished
processing the first interrupt. Immediately after the RTI instruction the controller will
renter the interrupt handler without executing an instruction in the main body of the
program.
Binder 4.3-01/03 Rev. B/495
Copyright  2003, EM Microelectronic-Marin SA
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