Page 10
Page 11
S
creens
The unit displays 32 characters from the PLC memory. These characters
are taken from the PLC data registers.
The unit tracks register DM0020 ( the Offset register ) in the PLC. The number
in DM0020 gives the start address of the data register block which contains the
characters to be displayed. For example, if DM0020 has number 124 in it, the
unit will read 16 registers from DM0124, i.e. from DM0124 to DM0139 and display
the corresponding characters.
Each register contains two bytes. Each ASCII character to be displayed is
one byte. So, each word contains two characters that can be displayed. All the
PLC ladder logic has to do is to put the correct words in the registers being read
by the unit so that a proper screen can be displayed.
As mentioned above, the starting address of the screen data block is
controlled by the Offset register, i.e DM0020. Hence, there can be two methods
of changing the screen to be displayed. One is to keep the value in DM0020
constant and change the data in the screen registers by the ladder logic. Second
is to keep the screen text in the data memory (by editing DM registers) and change
the value in DM0020 so as to point to the correct memory address to display the
desired screen.
It is possible to embed registers in the screens. The unit reads 16 registers
from DM0000 to DM0015 (in which DM0012 to DM0015 are used for Bar Graph)
in every scan. The data in these registers can be embedded in the screens. To
do so, use hex bytes 0 to B (C to F used for Bar Graph) corresponding to register
DM0000 to DM0011 respectively in the screen. Refer to the example given which
explains the embedding of registers. It is possible to embed one data entry field
in screens. It is similar to embedding register, only instead of 0 to F use 10 to 1F
hex bytes to address DM0000 to DM0015. The registers DM0000 to DM0015 can
be edited with this feature one at a time in a screen.
E
xample 1: Display a static screen
Suppose the following screen needs to be displayed on the
NT2S-SF123B-EV2 :
Last Rinse Cycle
Water pump is on
To display this screen, do the following:
a.
Move number 200 in DM0020 since the screen text will be stored
in DM0200 onwards.
b.
Move character string “Last Rinse Cycle” into 8 words from DM0200.
c.
In a similar manner, the characters “Water pump is on” can be embeded
into 8 words from DM0208. (i.e. from DM0208 to DM0215).
This will put the following data in data words below: ("b" is used for a space)
Word
ASCII
Hex
Word
ASCII
Hex
DM0200
La
#4C61
DM0208 Wa
#5761
DM0201
st
#7374
DM0209 te
#7465
DM0202
bR
#2052
DM0210 rb
#7220
DM0203
in
#696E
DM0211 pu
#7075
DM0204
se
#7365
DM0212 mp
#6D70
DM0205
bC
#2043
DM0213 bi
#2069
DM0206
yc
#7963
DM0214 sb
#7320
DM0207
le
#6C65
DM0215 on
#6F6E
