exactly two hexadecimal digits make up one byte, each hex digit representing 4 binary digits (4 bits) as shown
here;
Table 11: Hex Value Table
Binary Hex Decimal Binary Hex Decimal
0000
0
0
1000
8
8
0001
1
1
1001
9
9
0010
2
2
1010
A
10
0011
3
3
1011
B
11
0100
4
4
1100
C
12
0101
5
5
1101
D
13
0110
6
6
1110
E
14
0111
7
7
1111
F
15
Based on the table, the byte 01001011 can be represented in hex as 4B, which is usually written as any
of 4Bh, 4BH, 4B hex or 0x4B.
The numbers can also be expressed in decimal form if preferred.
7.3.1 ASCII Characters
Since computers deal internally with numbers only, but externally with both letters and numbers, several
schemes were developed to ’map’ written characters to numeric values. One such scheme has become
universal, the American Standard Code for Information Interchange, or ASCII. ASCII tables are readily
available from a number of sources. A few examples will do here;
Table 12: Example of an ASCII Table
The letter
A
Has a value of
65 Decimal or
41 Hex
The letter
A
Has a value of
97 Decimal or
61 Hex
The number
0
Has a value of
48 Decimal or
30 Hex
The number
9
Has a value of
57 Decimal or
39 Hex
This gives rise to the possibility of confusion when parameters are being set on the display. For example,
the GPO ON and OFF commands use a number to indicate which GPO is being controlled. We’re told that
acceptable values are 0 to 6. All such parameters must use numeric values (i.e., the actual byte values). If
we send the ASCII number 0 by mistake it will actually give the value 48 decimal (30 hex) to the parameter,
which is wrong.
In the tables given in the following sections ASCII characters are shown as ’A’, with single quotes.
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