Table of Contents
Advertisement
To accomplish this saving in scanning time and core
storage capacity, individual bits of the 6-bit binary-
coded-decimal
(BCD)
configuration in each core storage
location are used to record the status of the terminal
point contacts. In the first location, the first contact is
assigned to the 2 bit and the second contact to the 1 bit.
In the second through seventh positions, the first of
the three contacts is assigned the 4 bit, the second con-
tact is represented by the 2 bit, and the third contact
by the 1 bit, as shown in the following diagram.
Terminal
Points
37-39
BCD Bits
39------------------------------~
The corresponding bit is stored if a contact is closed;
the bit position is blank if the contact is open. For
example, if the first and third contacts are closed, the
core storage position assigned to the group of three
contacts contains a 4 bit and a 1 bit. Table 6 illustrates
this by showing the bit configuration for all possible
combinations of the three contacts when open and
Table 6. Bit Configuration of Closed Contacts
Terminal Contacts
37 - 39
BCD Bits of One Storage Position
Character
Core
37
38
39
C
4
2
Storage
C*
X
4
C
X
2
C
X
C
C
C
X
X
6
C
C
C
X
X
5
C
C
C
X
X
3
C
C
C
X
X
X
7
( none closed)
C
0
* Contact Closed
closed. The column on the right contains the corre-
sponding numerical designation of the combination
of bits stored according to the standard
BCD
notation
for 6-bit data storage. A closed or open contact may be
recognized as such by the program 2 to 5 ms after it
opens or closes.
Table 7 shows the distribution of the 20 points of
a group over the seven core storage positions designated
by the P address. The figures in the table are the nu-
merical representations of the bits stored as a result of
the related contacts being closed. Note that the loca-
tion P
1
records the status of two terminal point con-
tacts, while each of the remaining six locations reflects
the conditions of three terminal point contacts. As an
example, if it is desired to test for contact 14 being
open and contacts 15 and 16 being closed, a 3 is com-
pared with the data in
PH'
because terminal point con-
tacts 15 and 16 are the second and third contacts in that
location.
By selecting the proper number to compare with the
data in a given core storage location, the status of each
contact can be determined. In addition, where program
logic and process operation dictate, any combination of
two or three contacts in the same location can be tested
with one instruction. For example, an emergency con-
dition may be indicated if one of three blowers in a
hazardous area is not operating. This can be deter-
Table 7. Digits for Identifying Open and Closed Contacts for one
Terminal Address of 20 Terminal Contacts
Status of
Core Storage Positions
Terminal Points
1st
2nd
3rd
PI
P2
P3
P4
P 5
P 6
P 7
C*
2
4
4
4
4
4
4
C
2
2
2
2
2
2
C
C
C
3
6
6
6
6
6
6
C
C
5
5
5
5
5
5
C
C
3
3
3
3
3
3
C
C
C
7
7
7
7
7
7
Core Storage Position
* Contact Closed
47
Advertisement
Table of Contents
