Bits And Bytes - Omron SYSMAC C200H-ASC02 Operation Manual

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Bits and Bytes

2-1
Bits and Bytes
10
The PC's memory is divided up into many sections, each of which has its
own name and purpose. The ASCII Unit can access any of these memory
areas using the BASIC READ(@) and WRITE(@) statements (this is ex-
plained in more detail in Section 4 BASIC Language). However, there is a
special area in the PC's IR data area that is assigned to each ASCII Unit.
The MACHINE NO. switch on the front panel of the ASCII Unit (refer to Sec-
tion 1-1 Front Panel) is used to select one of the nine possible positions.
The PC's memory is organized into units called words. Information is usually
stored in word or multiple word units. Each word has a unique address in the
computer memory and can be accessed by specifying its address.
Each word contains 16 bits. A bit is the smallest piece of information that can
be stored or accessed by a computer. A bit is always either one or zero. Cer-
tain bits can be accessed individually and are used as flags. A flag is usually
set (1) or cleared (0) by the hardware to indicate some state of the computer
or to allow or disallow certain operations. Bits can also be set or cleared by
the programmer to communicate certain parameters or conditions to the
CPU.
For example: the ASCII Unit program requests data to be sent from the PC
using the BASIC GET statement; however, the PC has not yet collected the
data. The PC's Write FLAG is cleared to zero (0), indicating that the ASCII
Unit must wait. When the PC has collected the data, it sets the Write Flag to
one (1), signaling the ASCII Unit that it may proceed to read the data.
Section 2-1

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