The PLC-2/30 programmable controller data table can be separated into 6 distinct areas, assume the size of default data table has not been modified. These areas are:
• Timer/counter preset bit/word storage or values
• Timer/counter accumulated bit/word storage or values
• Area 1 of processor work
• Area 2 of processor work
• Table of input image
• Table of output image
The area of data table has 128 words of default size and is configurable from 48 - 8,064 words with 8K word memory or 8,192 words with the 16K word memory. This area saves the information required in the user program execution, for example status of input and output device, the status of internal storage points, and 3-digit numeric values.
Areas 1 and 2 of Processor Work
There are two areas of processor work: processor work area 1, the addresses are 0008 to 0078, and processor work area 2, the addresses are 1008 to 1078. These locations of memory can’t be accessed by the user. The word addresses are not presented for addressing. The processor utilizes both areas for functions of internal control.
Table of Output Image
The output image table primary is to control the outputs status wired to the modules output. If the table of output image bit is on, its communicating output is on. If the bit is cleared to off, its communicating output is off. These bits are managed by instructions in the user program. The processor organizes the bits status in the table of output image as it produces output commands. Actual hardware outputs amend state only if communicating table of output image bits adjust state or if they are forced.
The table of output image thus includes 256 bit addresses, or 16 word addresses. The table of output image can be decreased to 128 bit addresses (8 word addresses), or raised from 16 word addresses to 56 (896 bit addresses) using the industrial terminal. The 896 bit addresses correspond to the discrete outputs maximum number the processor can control by changing memory configuration to 896 I/O or seven 1771-A4B I/O chassis with 2-slot addressing. Each bit in the table of output image may be related with a terminal address of hardware, even though this is not always the problem, since a communicating output module may not really be placed in this slot of I/O rack. If it is, though, the address of terminal is the similar as the bit address. A secondary function of the table of output image is to supply for bits or words storage area. Bits and/or words in the table of output image not really used to save the devices on/off status can be utilized for data storage.