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2.
If
a memory interrupt is requested by the controller selector, 1 word time is taken
to service the request.
3.
Effectively, a BRS
0
is executed.
This operation requires
2
word times plus execution
of the program. Interrupt can take from 3 to 13 word times.
If
Alpha is the location of the instruction being executed when the program interrupt occurred,
then the BRS
0
performs the following:
1.
Alpha +1 is stored in location
0.
2.
The contents of location 1 is transferred to the P-register and program execution
started there.
The Program Interrupt Routine must begin with:
*
STF
LDQ
STD
STC
WSl
Count
WS2
WS3
Store special flip-flops
Load
Q
with new value
Store A and B
Store C
The Program Interrupt Routine must end with:
*LDC
LDD
LDF
BRU
WS3
WS2
WSl
0
x
Load C
Load A and B
Load special flip-flops
Return to point of interrupt
The Program Interrupt Routine will normally include execution of the Scan instruction. Also,
the worst case execution of the Program Interrupt Routine will be less than the time period
between program interrupts.
Thus, a program interrupt cannot occur while a Scan instruction
is being executed.
A program interrupt during an SCN instruction cannot be successfully done.
PROGRAMMING EXAMPLES, BIT BUFFER CHANNEL
The following example shows one method that might be used to receive one character from a
bit buffer. This method does not use the SCN instruction.
Location
Instruction
Symbol
OPR
Operand
Remarks
15530
ORG
7000
ORIGIN LOCATION 7000
15530
600000
REC VE
LDB
BIT?
BIT NUMBER SEVEN
15531
022001
NES
1
RECEIVE FIAG SET
15532
121531
BZE
~\--
l
NO, GO ·BACK
15533
042444
SRl
BR,B
YES, SHIFT NEW BIT TO B-REGISTER
15534
160000
BEV
RECVE+l
COMPLETE CHARACTER NOT IN, GO BACK
15535
026020
DEF
5
CHARACTER IN, RESET RECEIVE CLOCK
*
See "Instruction Repertoire" for detailed description.
@&IY&~rEIJ~ ~@------------
V-18
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