(040)
XFER #0010 S XXX
(187)
IOSP
(188)
IORS
0000
00
454
It is possible for the data in the CPU Bus Link Area, SYSMAC BUS/2 Area, CPU
Bus Unit Area, etc., to be changed by peripheral servicing between the execu-
tion of two instructions or even during the execution of an instruction accessing
many words. For example, if data is moved from XXXX in the CPU Bus Link Area
to words D
1
and D
2
in two consecutive MOV(030) instructions, the data in D
1
and
D
2
might be different if CPU Bus Link Area was refreshed between the execution
of the first and second MOV(030) instructions.
If an instruction changing many words in the CPU Bus Link Area such as
XFER(040) is executed while the CPU Bus Link Area is being refreshed, all of
the words might not be transferred to the peripheral unit at the same time.
The DISABLE ACCESS IOSP(187) and ENABLE ACCESS IORS(188) instruc-
tions can be used to ensure that the data being accessed is not simultaneously
accessed by peripheral servicing. In the example below, IOSP(187) and
IORS(188) are used to ensure that the ten words of data transferred to the CPU
Bus Link Area will be transmitted to the Peripheral Device at the same time.
Address Instruction Operands
00000 LD 000000
00001 IOSP(187)
00002 XFER(040)
#0010
s
XXX
00003 IORS(188)
If IOSP(187) is executed while the CPU Bus Link Area is being refreshed, ac-
cess to the CPU Bus Link Area won’t be stopped until the refreshing has been
completed. When XFER(040) is executed, CPU Bus Link Area refreshing will be
disabled. CPU Bus Link Area refreshing will be enabled by IORS(188) after the
10 words of data have been transferred to the CPU Bus Link Area.
PC Operation Section 6-1
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