Hardy HI 2151/30WC Single-Scale Controller - Manual (Page 21)

Chapter 5 - Block Transfers
5-1
CHAPTER 5 - BLOCK TRANSFERS
About Block Transfers The ladder logic programmer is able to exchange blocks of data with a
1/4 rack device via Block Transfer instructions in the ladder logic pro-
gram. A Write Block Transfer is used to send commands and data to the
Weight Controller, and a Read Block Transfer is used to collect
acknowledgments and data from the Weight Controller. It is recom-
mended that those front panel functions to be controlled via the Remote
I/O network be locked from front panel control. Consult the HI
2151WC manuals for more information.
To utilize 20 bit resolution, the Ladder Logic program must synchro-
nize the use of Block Transfer data to insure block integrity. Synchroni-
zation is accomplished by not using block data between the time block
transfer is enabled and done (EN and DN bits). Of course, data can be
moved to another buffer where it can be accessed while the next block
transfer is in progress. The structure of the four byte numeric format for
all weight parameters except totalized weight is as follows:
NOTE: The most significant word is located before the least significant word in the block I/O
transfer.
NOTE: Negative values are sent in “two’s complement” form.
NOTE: The maximum block size is 51 words.
NOTE: Block writes cannot be performed while the instrument is in the calibration mode. The
calibration must be sealed by pressing enter at Endcal.
Totalized weight uses all 32 bits available in the two words to represent
unsigned data. the block transfer commands and formats are listed in
the following tables. The Block Read commands are followed by the
Block Write commands. When writing information to the weight con-
troller be sure to send zeros (0’s) to all words and bits marked as
“reserved for future use”. This will aid in achieving upward compatibil-
ity to future enhancements to the command set. For additional informa-
tion on the function of each parameter in the tables below, consult the
HI 2151 Installation and Operation manuals.
Block Read Commands All block read commands are initiated by the ladder logic program per-
forming a block write to the weight controller with the desired block
command number in the first byte position of the block. the PLC then
performs a block read and the weight controller will return the desired
BYTE 1
BYTE 0
upper 4 bits Byte 0
lower 4 bits
BYTE 3 BYTE 2
Sign bits Sign bits
(all 1’s or 0’s) Weight bits
19-16 Weight bits
15-8 Weight bits
7-0
TABLE 5-1: FOUR BYTE NUMERIC FORMAT FOR WEIGHT PARAMETERS