ProSoft Technology MVI69-ADM - Manual (Page 51)

MVI-ADM ♦ 'C' Programmable Understanding the MVI-ADM API
'C' Programmable Application Development Module Developer's Guide
ProSoft Technology, Inc. Page 51 of 342
February 20, 2013
The module and the processor constantly monitor input and output images. How
does either one know when a new block of data is available? Recognizing a
change in the header information of the image (word 0) solves the problem. For
example, when the module recognizes a different value in the first word of the
output image, new read data is available. When the processor recognizes a new
value in the first word of the input image, new write data is available. This
technique requires the storage of the previously processed data block
identification code. The following illustration shows the normal sequence of
events for data transfer:
1 During program initialization, the write and read block identification codes are
set to one. The last block read variable is set to zero.
2 The program copies the first six-word block of the database starting at the
user defined Write Start Register to the input image (words 2 to 7). It then
sets the current read block code in word 1 of the input image. To "trigger" the
write operation, the program places the current write block code into word 0
of the input image.