Numbering System; Binary Code And Relative Terminologies - FATEK FBS Series Manual

1. Although using pointer register for indirect addressing application is powerful and flexible, but
changing the V and Z values freely and carelessly may cause great damages with erroneous
writing to the normal data areas. The user should take special caution during operation.
2. In the data register range that can be used for indirect addressing application (R0～R8071), the
328 registers R3840～R4167 (i.e. IR, OR and SR) are important registers reserved for system or
I/O usage. Writing at-will to these registers may cause system or I/O errors and may result in a
major disaster. Due to the fact that users may not easily detect or control the flexible register
address changes made by the V and Z values, FBs-PLC will automatically check if the
destination address is in the R3840～R4067 range. If it is, the write operation will not be executed
and the M1969 flag "Illegal write of Indirect addressing" will be set as 1. In case it is necessary to
write to the registers R3840～R4067, please use the direct addressing.

5.3 Numbering System

5.3.1 Binary Code and Related Terminologies
Binary is the basic numbering system of digital computer. Since the PLC operates with discrete ON/OFF values, it is
natural to use binary codes. The following terminologies should be fully understood before go to further topic of
numbering system.
● Bit: (Abbreviated as B, such as B0, B1, and so on) It is the most basic unit of binary value. The status of bit is either
"1" or "0".
● Nibble: (Abbreviated as NB, such as NB0, NB1, and so on）It is formed by four consecutive bits (e.g. B3～B0) and
can be used to represent a decimal number 0～9 or a hexadecimal number 0～F.
● Byte: (Abbreviated as BY, such as BY0, BY1, and so on) It is formed by two consecutive nibbles (or 8 bits, such as
B7～B0) and can be used to represent a 2-digit hexadecimal number 00～FF.
● Word: (Abbreviated as W, such as W0, W1, and so on) It is formed by two consecutive bytes (or 16 bits, such as B15
～B0) and can be used to represent a 4-digit hexadecimal number 0000～FFFF.
● Double Word: (Abbreviated as DW, such as DW0, DW1, and so on) It is formed by two consecutive words (or 32 bits,
such as B31～B0) and can be used to represent an 8-digit hexadecimal number 00000000～FFFFFFFF.
BY3
NB7 NB6
B31 B30 B29 B28 B27 B26 B25 B24 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
W1
BY2
NB5 NB4

Warning
DW
BY1
NB3 NB2
5 - 9
W0
BY0
NB1 NB0
←Double Word
←Word
←Byte
←Nibble
←Bit