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A byte represents an eight-bit binary number (11111111),
therefore each byte can represent eight I/O lines. Each bit is
assigned a bit position and a weight (value). Refer to Table 3.3.
Table 3.3 - Bit Assignments for I/O Lines
MOST SIGNIFICANT I/O BYTE
I/O Line #
15
14
13
Bit Position
7
6
5
Hex Weight
80
40
20
Dec. Weight
128
64
32
LEAST SIGNIFICANT I/O BYTE
I/O Line #
7
6
5
Bit Position
7
6
5
Hex Weight
80
40
20
Dec. Weight
128
64
32
To set an output to a HIGH state the corresponding bit position
must be set to a "1". Conversely to set an output LOW the
corresponding bit position must be set to a "0". When reading I/O
lines, any bit set to a "0" indicates the corresponding I/O line is in
the LOW state and any bit set to a "1" indicates the corresponding
I/O line is in the HIGH state.
Example 3.1 - To set outputs 15, 8, 1, and 0 to a HIGH state, and all
other outputs to a LOW state (shown in bold face) -
MS Byte
Shown in binary -
10000001
Shown in decimal -
129
(128+1)
Shown in hexadecimal -
81
(80h+1h)
Example 3.2 - Reply from Read I/O command (shown in bold face) -
MS Byte
Shown in binary -
11001000
Shown in decimal -
200
(128+64+8)
Shown in hexadecimal -
C8
(80h+40h+8h)
I/O lines #15, 14, 11, 6, 4, 1 are HIGH. All other I/O lines are LOW.
232SDD16-1005 Manual
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
12
11
10
9
8
4
3
2
1
0
10
8
4
2
1
16
8
4
2
1
4
3
2
1
0
4
3
2
1
0
10
8
4
2
1
16
8
4
2
1
LS Byte
00000011
3
(2+1)
3
(2h+1h)
LS Byte
01010010
82
(64+16+2)
52
(40h+10h+2h)
11
Read I/O Lines Command
The Read I/O Lines command returns two data bytes that reflect
the state of the I/O lines. The first data byte contains the most
significant I/O lines (15 - 8). The second data byte contains the
least significant I/O lines (7 - 0). If a bit is a "0" then the state of that
I/O line is LOW. If a bit is a "1" then the state of that I/O line is HIGH.
Command: !0RD
Argument:
none
Response: the state of the 16 I/O lines in two 8 bit bytes (shown in
bold face)
ASCII Example: !0RDÈR
Dec. Example: !0RD<200><82>
Hex. Example: !0RD<C8><52>
Bin. Example: !0RD<11001000><01010010>
Description: the first byte indicates that I/O lines #15, 14, & 11 are
HIGH and I/O lines # 13, 12, 10, 9, & 8 are LOW; the second byte
indicates that I/O lines # 6, 4, & 1 are HIGH and I/O lines # 7, 5, 3, 2,
& 0 are LOW.
Set Output Lines Command
The Set Output Lines command is used to set the states of the
output lines. This command requires two data bytes. These data
bytes specify the output state of each output line. The first data byte
represents the most significant I/O lines (15 - 8). The second data
byte represents the least significant I/O lines (7 - 0). If a bit position
is set to a "0" then the state of that output line will be set LOW. If a
bit position is set to a "1" then the state of that output line will be set
HIGH.
NOTE: Refer to the "Define I/O Lines" command to define an I/O line
as an output.
12
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
232SDD16-1005 Manual
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