User guide

Hardware
890 USE 108 00 August 2001 19
Space Allocation
Formula for Data
Types
The maximum of each data type expressed in System Capacity, p. 18, or the E984-
258/265/275/285 PLCs fit into the total configured memory space according to the
following formula: A+B+C+D+E+F <= 65024 words for 64k State RAM or 32256
words for 32k State RAM or 15872 words for 16k State RAM (and the combined mix
of configured #0x +#1x <= 65536 or 32768 or 16384) Where: A =Number of (0x/
16) * 3 to include History and Disable bits B=Number of (1x/16) * 3 to include History
and Disable bits C=0 if starting 3x on a 16 word boundary, otherwise add the
required difference D=Number of 3x data types E=0 if starting 4x on a 16 word
boundary, otherwise add the required difference F=Number of 4x +(2*((#4x+15(/16))
to include Up/Down counter history
Executive Non-
Volatile ROM
FLASH Memory
and RAM
(E984’s Only)
The Compact executive firmware has two areas of memory which are referred to in
this manual as executive and user memory. The executive is contained in Non-
Volatile ROM (flash in the E984s memory that can be updated with new features in
the field if required), and the user memory is stored in battery backed RAM which
may also be backed up to internal FLASH for the E984-258/265/275/285 models or
to the PCMCIA memory card for the E984-275/285 models. (See Customer Service
& Technical Assistance, p. 219 regarding upgrading the NV FLASH Memory in the
field).
EEPROM
Auxiliary
Memory Upload-
Download
Capabilities
(A984-1xx, E984-
24x/251/255
Only)
The A984-1xx, and E984-24x/251/255 Compact Controllers contain an auxiliary
memory socket for a credit card-sized EEPROM card. You can write the current
system configuration and user logic program to an EEPROM card while the
controller is in STOP Mode and read the data back to the controller from the
EEPROM card as part of the power-up sequence. This utility allows you to record,
store, transport and reload applications and configuration with an easily
maintainable medium. Thus this EEPROM may be used on similar compact models.
Note: For the A984-120/13x/14x and E984-24x/251/255 models. The listed values
(in the table). See System Capacity, p. 18 for discrete (0xxxx, 1xxxx) and register
(3xxxx, 4xxxx) types represent maximum allowable. To maximize one type you
minimize the other three types. Other than these limits the allocation between data
types is flexible. This type of trade off between reference types does NOT apply to
the E984-258/265/275/285 models. Furthermore, due to the large memory size
you will not reach the maximum limits.
Note: Maximum I/O module count is 18 for all Compact PLC models.