Data Table
Chapter 3
317
The message storage area begins after the END of user program statement
and it stores the alphanumeric characters of the messages.
The memory is capable of storing user-programmed messages for
hardcopy printout by compatible RS-232C data terminals. As many as 70
messages of varying length can be stored (198 messages can be stored
when using the 1770-RG Report Generation module).
Message storage immediately follows the END (of program) statement,
and is limited only by the number of unused words remaining in memory.
Each word remaining after the END statement is capable of storing 2
ASCII message characters. (Characters are defined as keyboard entries
made on the data terminal, such as A, 1, M, ., 8, space, etc.)
Messages are stored in numerical order. Messages 1 through 6 are
controlled by word 0278 and have the highest priority. The next 8
messages are controlled by the first user-designated message control word,
the next 8 in the second control word, etc. Eight consecutive words can be
reserved as message control words. (When using the 1770-RG module, 24
consecutive words can be reserved.)
WARNING: Bit addresses 02710
8
thru 02717
8
and all the bits
in the upper byte of the message control words may be used for
automatic report generation functions. Since the user program
examines these bits to determine report generation status
and may also set them to initiate various report generation
operations, these bits should not be used for other functions.
These words should also be reserved.
It is important to understand how machine data, sensed by the input
modules, is used by the processor to turn output devices on or off. The
hardware-program interface occurs in the input/output image tables.
The primary purpose of the input image table is to duplicate the status (on
or off) of the input devices wired to input module terminals. If an input
device is on (closed), its corresponding input image table bit is on (1).
If an input is off (open), its corresponding input image table bit is off (0).
Input image table bits are monitored by user program instructions but are
controlled by the input devices.
The primary purpose of the output image table is to control the status (on
or off) of the output devices wired to output module terminals. If an output
image table bit is on (1), its corresponding output device is on (energized).
3.2.3
Message Storage Area
3.3
Hardware/Program Interface
3.3.1
Image Tables
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