Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 48)

Operating Functions
Chapter 5
5–11
5.3.11.1 RAM
When you enter RAM(cr), the BASIC Module
selects the current
program from
RAM MEMORY.
Important: RAM
space is limited to 13 K bytes. Use the following
formula
to calculate the available user RAM space:
LEN system
control value which contains current RAM
program length
+# bytes allocated
for strings (first value in the STRING
instruction)
+6 * each array
size + 1 (asterisk = multiply)
+8 * each variable
used (including each array name)
+1024
V – number of
bytes reserved for BASIC
Available
user RAM= MTOP–V
5.3.11.2 ROM
When you enter ROM [integer],
the BASIC Module selects the current
program out
of EPROM memory. If no integer is typed after the
ROM command (i.e.
ROM) the module defaults to ROM 1. Since the
programs are
stored in sequence in EPROM, the integer following
the ROM command
selects which program the user wants to run or
list. If you attempt
to select a program that does not exist (e.g. you type
in ROM 8 and only
6 programs are stored in the EPROM) the
message ERROR: PROM MODE is
displayed.
The module
does not transfer the program from EPROM to RAM when
the
ROM mode is selected. If you attempt to alter a program in
the ROM mode, by typing in a line
number, the message ERROR:
PROM MODE displays.
The XFER command allows you to transfer
a program from
EPROM to RAM for editing purposes. You get no
error message if
you attempt to edit a line of ROM program.
Important: When
you transfer programs from EPROM to RAM you
lose
the previous RAM contents.
Since the ROM command does NOT transfer a program to RAM, it
is
possible to have different
programs in ROM and RAM simultaneously.
You can
move back and forth between the two modes when in
command mode. If you are in run mode you can change
back and forth
using CALLS 70, 71 and 72. You can also use all of the RAM memory
for variable storage if the program is stored in EPROM. The
system
control value – MTOP always refers
to RAM. The system control value,
LEN, refers
to the currently selected program in RAM or ROM.
5.3.11
Commands: RAM and ROM
[integer] (continued)