ZX Hard #00 31 августа 1998

Железо

Interrupts Spectrum'e - scheme for IM2 interrupts.

        Interruption in Spectrum'e


(C) VTS'98


I'm here somewhere (sorry, can not remember) read
resentment of the fact that the Spectrum has only
one level of privilege to interrupt ... But excuse me, but what 
IM2? After all, with Use it to organize have 7

priority levels (excluding normal
polukadrovogo INT'a)! So even with a
pleasing to the organization of priorities, because
Mounting plate is programmed into the RAM!

Those who have no manual for the Z80, explain.

1.Intovaya plate shall begin on
address with ml.baytom = # 01. As always, the low byte of the 
address processing procedure of interruption - at the lowest 
address. Length of the table - 256 (B) -> 128 addresses. 

2. When you receive interrupts (input INT /
Nemo-bus) processor takes its (programmnodostupny) I register 
as a high byte, and the fact that he had received over the data 
bus (after issuing a signal INTA / = IORQ / OR M1 /) as a 
junior, and upon receipt of the address read from the interrupt 
handler address labels. 

! Attention! D0 must be free,
(Therefore = 1) to uniquely identify the address of the 
transition. 

At first glance, this gives 128 possible
requests without priority.
On the second - 7 requests with priority.


IORQ / a INTA / LP8, AP6, etc.

  M1 / m / s or OK

                          Z-state.

                    oEO /

                     -
      IRQ1 /> D1



      IRQ2 / D2

        . . . .

        . . >. .


      IRQ7 / D7



REM> not shown the formation of INT'a (QA elements or diodes):


         LP9

IRQ1 / |> INT / IRQ1 / |  IRQ2 / | <

. . . . . .


On the plate. For example, take the IRQ1, IRQ2
and IRQ3. All the rest - are inactive, ie
set to 1. Register I = # 80.

hex
....
80f1
80f2 processing IRQ3 + IRQ1 + IRQ2

80f3
80f4 processing IRQ3 + IRQ2

80f5
80f6 processing IRQ3 + IRQ1

80f7
80f8 processing IRQ3

80f9 processing IRQ1 + IRQ2
80fa

80fb processing IRQ2
80fc

80fd processing IRQ1
80fe

80ff processing INT 50Hz with the lowest
8100 priority.
....

In addition, to determine if polukadrovogo INT'a with other 
IRQ, unfortunately, not possible (and necessary?). 

Hopefully, no more questions?.

PS: And if they need the most interruptions :-)? Vaughn has 
much every peripheral on the Spectrum - and nobody come in 
handy ;-). So it should not succumb corrupting Western 
influence and to continue use their original and unique 
solutions [:-) M 


11.08.98 16:37 msk is-dos