Binary Data Line Values Using Hdat Strobe; Bcd Data Line Values Using Hdat Strobe - Allen-Bradley A-B QUALITY DL20 Series User Manual

Chapter 7
The Parallel Port
Using the
Parallel Port
7–6
Table 7.E

Binary Data Line Values Using HDAT Strobe

Data Line
D0
D1
D2
D3
D4
D5
D6
D7
D8 D8 and D9 are not used when variable data is strobed in.
D9
The value is the sum of D0 through D6: D0 + D1 + D2 + D3 + D4 + D5 +
D6 = Value. The seventh wire, D7, is called the sign bit -- numbers can be
positive or negative. The value read during the LDAT strobe is added to the
value read during the HDAT strobe to obtain the value of the variable from
-32,768 to +32,767. Negative numbers are interpreted as two's compliment
values by the DL20 and should be transmitted that way. Most programmable
controllers use two's compliment values and no conversion is required.
In the BCD numbering system, the data lines are also interpreted differently.
When the HDAT portion of the variable is being strobed in, the lines still
represent two BCD digits; this time the digits are the hundred and thousand
places of the desired variable. Table 7.F defines the new digit weights:
Table 7.F

BCD Data Line Values Using HDAT Strobe

Data Line
Data Line Value
D0 100
D1 200
D2 400
D3 800
D4 1000
D5 2000
D6 4000
D7 8000
D8
D9
Value
256
512
1024
2048
4096
8192
16384
Sign Bit: 0 = Positive 1= Negative
Set both lines to 0. in s
Comment
Hundreds Digit (0-9) Hundreds Digit (0-9)
Thousands Digit (0-9) Thousands Digit (0-9)
D8 and D9 are not used when
variable data is strobed in. i is s in
Set both lines to 0.