8x300 design guide - Al Kossow's Bitsavers - Trailing-Edge

In total, eight interupt requests may be given. As an example,
INTREQA is chosen as an edge-trigger interrupt while INTREQH is
treated in a handshake procedure.
The eight interrupt request signals, INTREQA through INTREQH,
either trigger an interrupt flip-flop or feed directly into a masking
gate, with which it is possible to inhibit one or more chosen levels.
G-
0-
7474
INTFPA
A- - C
INTREO _ 0 _
'5V
R
rc:.. ............. 1_.1..,-,1 INTERRUPT SIGNAL
I }- 7
r--------L...._,~
I
I
I
I
I
I
I
I
I
I
I
I
I
- 6
EO GS
CLEAR
- 5 - 40 40 ........
MCLK -
l
INTERRUPT ~
CODE
- -=-
-4 A2 f--- 3D 301---+--1-+-1 A
-3
-2
I
...
-1
or+~~~~+-D-' O
RESET--_--
INT
MASK
74148 74175
__ ~~
El
+--,
1 -'-
~ -
I \
'T~
I
I
I
_1-
INTERRUPT
INHIBIT
A1 ~ 20
A0t-- 10
CLOCK
201---~+-IB
101----~C
G2A
7413B
I
C
7474
ACKN-H - -H
o S 0 f-
~""""",,""'I
G2B~
Y7
I
I
I
I
I
;
1
G1 YO~~t---- AA
T ~
~ ______---1 ACKNOWLEDGE
INTERRUPT
ACKNOWLEDGE
1
I
1
I
1
Figure 2-38. Priority Interrupt Level Logic
INT MASK signals come from an I/O port, so that masking may be
done by software. A general interrupt inhibit may be applied if a
signal is fed to the EI input of the encoder. If this is not requried,
the EI input should be tied to ground. The priority of the incoming
interrupts is determined in the priority encoder. If at least one
interrupt request is active at the input of the encoder, an
INTERRUPT signal is generated for the Interrupt Control (Figure
2-32). The code of the acti ve interrupt with the highest priority is
clocked into the flip-flops of the 74175, coincident with the
INTERRUPT ACKNOWLEDGE from Interrupt Control.
2-57