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Hello all,

After reading some docs,i have some dark points about the
the IRQ_LINE and the IRQ_VECTOR ?

I suppose that the IRQ_LINE is the irq mode of the Z80 (0->2) and the IRQ_VECTOR is the address where the PC must jump.
Am i right ?

Tia

Quote

> I suppose that the IRQ_LINE is the irq mode of the Z80 (0->2) and the IRQ_VECTOR is the address where the PC must jump.
> Am i right ?

The interrupt mode can only be set by a software instruction (like im 1, im 2, etc.)

The IRQ line is a pin on the Z80 chip which other devices can use to cause an interrupt.
It doesn't affect the interrupt mode.

You're right about the interrupt vector.

In the case of the SMS, it's always 0x38, but for some games
that use IM 0 and want to read data off the bus, the return
value is 0xFF. (which is just a rst 38h instruction if memory serves)

Author	Message
Kroustibat Guest	Basics questions Posted: Thu May 18, 2000 10:30 am
Kroustibat Guest	Hello all, After reading some docs,i have some dark points about the the IRQ_LINE and the IRQ_VECTOR ? I suppose that the IRQ_LINE is the irq mode of the Z80 (0->2) and the IRQ_VECTOR is the address where the PC must jump. Am i right ? Tia

Charles MacDonald Joined: 28 Sep 1999 Posts: 1197	Posted: Thu May 18, 2000 4:17 pm
Charles MacDonald Joined: 28 Sep 1999 Posts: 1197	Quote > I suppose that the IRQ_LINE is the irq mode of the Z80 (0->2) and the IRQ_VECTOR is the address where the PC must jump. > Am i right ? The interrupt mode can only be set by a software instruction (like im 1, im 2, etc.) The IRQ line is a pin on the Z80 chip which other devices can use to cause an interrupt. It doesn't affect the interrupt mode. You're right about the interrupt vector. In the case of the SMS, it's always 0x38, but for some games that use IM 0 and want to read data off the bus, the return value is 0xFF. (which is just a rst 38h instruction if memory serves)

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