Rockwell Automation Allen-Bradley Micro850, Оригинальное руководство пользователя

Страница: 74 / 290

74 Rockwell Automation Publication 2080-UM002L-EN-E - November 2021
Chapter 6 Program Execution in Micro800
Variable Retention
After a power cycle, all variables inside instances of instructions are cleared.
Micro830 and Micro850 controllers retain all user-created variables. Micro810®
and Micro820 controllers can only retain a maximum of 400 bytes of user-
created variable values. Micro870 controllers can only retain a maximum of 128
kilobytes of user-created variable values.
For example: A user-created variable called My_Timer of Time data type will be
retained after a power cycle but the elapsed time (ET) within a user-created
timer TON instruction will be cleared. This means that after a power cycle,
global variables are cleared or set to initial value, and depending on the
controller, some or all user-created variable values are retained. You can
choose which variables to retain by selecting them on the global variable page.
Memory Allocation
Depending on base size, available memory on Micro800 controllers are shown
in the table below.
These specifications for instruction and data size are typical numbers. When a
project is created for Micro800, memory is dynamically allocated as either
program or data memory at build time. This means that program size can
exceed the published specifications if data size is sacrificed and vice versa. This
flexibility allows maximum usage of execution memory. In addition to the
System Variables for Scan and Power-up on Firmware Revision 2 and later
Variable Type Description
_SYSVA_FIRST_SCAN BOOL
First scan bit.
Can be used to initialize or reset variables immediately after
every transition from Program to Run mode.
Note : True only on first scan. After that, it is false.
_SYSVA_POWER_UP_BIT BOOL
Power-up bit.
Can be used to initialize or reset variables immediately after
download from Connected Components Workbench or
immediately after being loaded from memory backup module
(for example, microSD™ card).
Note : True only on the first scan after a power-up, or running a
new ladder for the first time.
Memory Allocation for Micro800 Controllers
Attribute
10/16-point
(Micro830)
20-point
(Micro820)
24- and 48-points
(Mico830, Micro850)
24-point
(Micro870)
Program steps
(1)
(1) Estimated Program and Data size are “typical” – program steps and variables are created dynamically.
1 Program Step = 12 data bytes.
4 K 10 K 10 K 20 K
Data bytes 8 KB 20 KB 20 KB 40 KB