What The Scanner Does 1 - Allen-Bradley 1784-KTX Reference Manual

Chapter 1
Understanding I/O Scanner Concepts
Allen-Bradley Parts
1-4
Here is an example layout of the output image table showing the first
8 racks:
word # 0
(hex) rack
00-07 0 xxxx
08-0F 1 xxxx
10-17 2 xxxx
18-1F 3 xxxx
20-27 4 xxxx
28-2F 5 xxxx
30-37 6 xxxx
38-3F 7 xxxx
The word numbers above can be used as subscripts. (We'll look closely at
that in chapter 6, Discrete I/O.) Each 16-bit word corresponds to 16
discrete I/O terminal positions, terminal 17 octal (15 decimal) to the
high-order bit and terminal 00 to the low-order bit.
Just as each I/O group has an address, so does each adapter. Adapter
addresses are used in the scan list (see page 1-6, What the Scanner Does).
The adapter address is the address of the first I/O group covered by the
adapter, divided by 2. This is numerically the same as (rack x 4) + (starting
group / 2), where the rack and group are both numbered from 0 through 7
as shown above. If you prefer, you can think of 1/4 racks being numbered
from 0 through 3, and then the adapter address is (rack x 4) + (quarter).
A slot is a position in an I/O chassis for one I/O module. In 1-slot
addressing, an I/O group represents a single slot. In 2-slot addressing,
an I/O group represents two slots.
Logical Rack / Starting Quarter and Link Addresses
Adapter link addresses are composed of a rack number concatenated with a
starting quarter for a given rack. The two low-order bits of the address are
the starting quarter of the rack, and the next 5 bits are the rack address.
The high bit is always zero when using the KTx.
Example: rack 7, starting quarter 3 has a link address of 00011111binary,
or 1F hexadecimal. In viewing the binary representation, the address
breaks down as follows: 0 – 00111 – 11. The high order bit is 0, the rack
address is 00111, and the starting quarter is 11.
Examine the examples on page 1-5.
Group
1 2 3 4
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
xxxx xxxx xxxx xxxx
5 6 7
xxxx xxxx xxxx
xxxx xxxx xxxx
xxxx xxxx xxxx
xxxx xxxx xxxx
xxxx xxxx xxxx
xxxx xxxx xxxx
xxxx xxxx xxxx
xxxx xxxx xxxx