TM 5-6675-323-14
(6) The computer interrupt logic circuit allows the HP-IB Interface to
Before it can transfer data to the
request service, i.e., talk to the computer.
computer, the HP-IB Interface must first notify the computer and request a transfer.
This circuit has two interrupt request lines to the computer, IRL and IRH. When an
i n t e r r u p t is required, as when data from the HP-IB is to be processed, the processor
in the control logic circuit outputs a computer interrupt request (CIRQ) instruction
s i g n a l t o t h e c i r c u i t . This signal induces the circuit logic to send an IRL or IRH
s i g n a l l o w . W h i c h signal goes low depends on which address the select code switch
If the switch is set between and 7,
in the select code decoder circuit is set.
IRL is sent low.
I f the switch is set between 8 and 15, IRH is sent low. When the
computer senses an interrupt request, i t w i l l c o n d u c t a n i n t e r r u p t p o l l t o d e t e r m i n e
w h i c h o f i t s i n t e r f a c e s r e q u i r e s s e r v i c e . A peripheral address bit (PA thru PA3)
will be received from the computer by the select code decoder circuit of the HP-IB
Interface.
If the bit matches the setting of the select code switch, then the
transfer cycle previously described is initiated in reverse and data in the I/O data
register circuit is transferred to the data lines. The computer interrupt logic
circuit will also pull one of the I/O data lines low.
NOTE
For a select code switch setting of 7, data line I0D7 should be
low.
See Table 3-3 for a complete list of interrupt request bits.
Table 3-3.
INTERRUPT REQUEST BITS
Select Code
L i n e Pulled Low
or8
IOD
IOD1
1or9
2 or 1
IOD2
IOD3
3 or 11
4 or 12
IOD4
IOD5
5 or 13
IOD6
6 or 14
IOD7
7 or 15
(7) Communication between computer and plotter. The computer interrupt
logic circuit allows the plotter to become the active controller and interrupt
operation of the processor in the control logic circuit. The interrupt logic is
enabled by an interrupt enable (IENA) signal from the control logic circuit.
3-13
