Rockwell Automation 6008-SV2R VMEbus remote I/O Scanner - Manual (Page 13)

Chapter
Scanner Overview
1
1Ć5
These VMEbus transfers are asynchronous to the scanner’s I/O update.
This means there is no way to know exactly when the data being put in the
output image table will be sent to the appropriate I/O rack. Data is sent to
an adapter only when that adapter is being scanned. Best-case timing is if
the data is placed in the output image table just before the specified adapter
is scanned; worst-case timing is if the data is placed in the output image
table just after the specified adapter was scanned. In the worst-case
scenario, the data does not reach the specified I/O rack until the next time
that adapter is scanned.
How the Scanner Responds to VME Signals
The scanner can generate interrupts on any of seven request levels
(IRQ1-IRQ7). When a VMEbus master acknowledges the interrupt, the
scanner replies with a vector (status/id) using the odd 8 bits of the data bus.
Important: The VME master processor might “crash” if there is no
software routine written to process an interrupt from the scanner. Or, you
can use the SETUP command to configure the scanner so that it never
generates interrupts, in case no interrupt software routine has been written.
If the scanner does not generate interrupts, the application program must
“poll” the scanner to see when commands have been processed.
The scanner responds to Data Transfer Bus (DTB) cycles initiated by
masters that transfer data 16 bits at a time or 8 bits transferred in an even
and odd format (D16, D08EO). The scanner works in the 16-bit (short)
addressing mode or the 24-bit (standard) addressing mode.
The scanner responds to common VME signals as follows:
This VME
signal:
means:
SYSFAIL When the scanner recognizes a SYSFAIL signal, it can either ignore the signal or
shut itself down, depending on how the scanner is configured. When the scanner
shuts down, the I/O serviced by the adapter either resets to a default condition or
holds all of its current values, as determined by switches on the I/O chassis
backplane. When the scanner is faulted or shut down, it asserts SYSFAIL on
the VMEbus.
ACFAIL When the scanner recognizes an ACFAIL signal, it shuts itself down because this
means that power will soon be gone. When the scanner shuts down, the I/O
serviced by the adapter either resets to a default condition or holds all of its
current values as determined by switches on the I/O chassis backplane.
SYSRESET If SYSRESET is asserted on the VMEbus, the scanner resets itself and goes
through its initialization tests. The scanner does not clear (reset to 0) the input
and output image tables. After a SYSRESET signal, you have to wake up the
scanner, the same as a powerĆup situation.