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6-1-2 Asynchronous Operation
The CV-series PCs can execute instructions and refresh I/O in parallel with
peripheral servicing (CPU Bus Units, Host Link Units, etc.). Peripheral servic-
ing will access data in the Link Area, SYSMAC BUS/2 Area, CPU Bus Unit
Area, and CPU Bus Link Area completely independently of program execu-
tion timing. This independent parallel processing is called asynchronous op-
eration.
Normally, instruction execution and peripheral servicing are independent,
however, an event processing request from a Unit is synchronized with pro-
gram execution. The cycle time for asynchronous operation is the time re-
quired for instruction execution.
Basic processes
Cycle time and
Event processing
Write I/O memory
Write program
Read program
Monitoring
Forced Set/Reset
processing
Program execution
Refresh timers
Input and output refreshing
Basic processes
CPU Bus Unit servicing*
Peripheral Device servicing
Host interface servicing
CPU bus check
Memory check
Battery check
Clock update
Start input check
Unit #0 refreshing
Unit #0 event processing
Unit #15 refreshing
Unit #15 event processing
Event
processing
request
Interrupt processing:
SYSMAC NET Link refreshing
SYSMAC LINK refreshing
SYSMAC BUS/2 refreshing
CPU Bus Link refreshing
Interrupt processing:
I/O Interrupt program
Scheduled interrupt program
SYSMAC BUS refreshing
TIMH(015) refreshing (every 10 ms)
Scheduled refreshing
Timer refreshing (every 80 ms)
I/O bus check
Program Execution Peripheral Servicing
memory check
Note *Only BASIC Units and Personal Computer Units are refreshed in CPU Bus Unit
servicing. Other CPU Bus Units are refreshed in interrupt processing.
When the PC is in asynchronous operation, instruction execution and peripheral
servicing accesses I/O memory independently.
Instruction Execution
PC Memory
Peripheral servicing
Read
Write
Write
Read
Programming Precautions
PC Operation Section 6-1
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