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90
Data Exchange Time Charts
Section 6-4
6-4-8 Combined IOWR (#CC00), IORD (#00
@@
), ON PC GOSUB, and PC
EPUT Timing
The IOWR (#CC00) instruction sends an interrupt to the ASCII Unit. The inter-
rupt subroutine is executed immediately andwrites to the shared memory
using the PC EPUT command. At the next I/O refresh period, the completion
of the interrupt subroutine is transferred to the CPU Unit, and at the next cycle
data is transferred by the IORD (#00
@@
) instruction.
6-4-9 Sending Interrupts from CPU Unit to ASCII Unit: PC Interrupts
There are two methods for sending PC Interrupts as described below.
Using PC Interrupt Bit The CPU Unit sets an interrupt number in the ASCII Unit in the allocated
words in the IR/CIO area. When the PC Interrupt Bit turns ON, an interrupt is
sent. The ASCII Unit executes the interrupt subroutine if the interrupt number
is the same as the ON PC command interrupt number. When the interrupt
subroutine has been completed, the Interrupt Subroutine Completed Flag is
toggled (OFF to ON or ON to OFF).
U
ASCII Unit
CPU Unit
ON PC
GOSUB
R N
IORD (#00
@@
)
Transfer by the IOWR
instruction
Subrou-
tine
branch
IOWR (#CC00)
PC EPUT
Completion of
the interrupt
subroutine
Interrupt subroutine
RETURN
CPU Unit ASCII Unit
n + 2 n + 2
n + 5 n + 5
PC Interrupt Bit
Interrupt by the
allocated I/O
Interrupt
number
(01 to 99 BCD)
At I/O refresh
Toggles after completion
of the subroutine
n
Bit 04
n
At I/O refresh
PC Interrupt Subroutine Completed Flag
7 0
Bit 01
Bit 04
7 0
Bit 01
ON PC
a
a
GOSUB
MOV
Interrupt No.
n+2
PC Interrupt Bit
a
PC
ON