2
2-9
GFK-1044A
Chapter 2 Installation and Initialization
The Initialization Process
Initialization must always be performed by a VME bus master module.
Addressing the Target VME DLAN Module
Once values have been assigned to the initialization data, it may be written to VME dual-ported
memory in the DLAN module. The VMEbus interface of DLAN modules always responds to
read and write requests in VME short non-privileged mode, but only the first 2K (800 hexadeci-
mal) bytes of dual-ported memory may be accessed in this mode. Accordingly, the principal
use of short non-privileged mode with VME DLAN modules is to detect their presence and
write initialization data to them.
Writing Initialization Data
The initialization data must be written to a 64 byte block of VME dual-ported memory in the
target module, starting at offset 40 hexadecimal (64 decimal) from the starting address shown in
table 2-1, and using the address modifier code 29 hexadecimal and 8 bit (D8) data access. The
data must be copied sequentially, starting at its low order address, so that the flag at byte offset
3F hexadecimal (63 decimal) of the data (that is, offset 7F hexadecimal, or 127 decimal, from
the start of VME dual-ported memory) arrives last. This byte signals the DLAN module that
the setup data it has been waiting for is now available.
Caution
With some VME CPU modules, failure to use 8 bit (D8) data transfers
when writing initialization data to the DLAN module will cause the byte
order of the data in the DLAN module to be reversed. When this
condition occurs, module initialization always fails, and the Module OK
LED continues to flash indefinitely.
If the data is written too soon after the DLAN module is powered on, the new values will ap-
pear to be VME memory test errors and will prevent the module from operating. The initializ-
ing application must wait until the target module is ready before writing setup data. When the
module is ready, a zero value will appear in the byte at offset 7F hexadecimal (127 decimal)
from the start of VME dual-ported memory. The byte must be read in short non-privileged
mode.
Reading the DLAN Module’s Acknowledgment
The success or failure of the initialization process may be determined by reading the byte at
offset 7F hexadecimal (127 decimal) from the start of VME dual-ported memory in the DLAN
module. The byte should be read using standard non-privileged mode (Address Modifier code
39 hexadecimal) and the module start address obtained by multiplying the byte value that was
written to byte offset 5 of setup data by 64K (10000 hexadecimal). The expected value is 0FF
hexadecimal (255 decimal).
The interval between the time when setup data is written and the time when the status value
indicates success will usually be a few hundred microseconds. If the standard non-privileged
