User guide

Software
62
890 USE 108 00 August 2001
SAVE Instruction
Block
(E984-258/265/
275/285 Only)
The SAVE block saves a block of 4x registers to state RAM. State RAM protects the
registers from unauthorized modification.
The size is three nodes
The PLC compatibility is PC-E984-258, PC-E984-265, PC-E984-275, and PC-
E984-285.
The opcode is 54 hex
The following figure shows the block structure of the SAVE block.
Inputs
SAVE has one control input that starts the operation and it should remain ON until
the operation has completed successfully or an error has occurred.
Outputs
SAVE may produce two possible outputs. The outputs from the top node goes
ON while a SAVE operation is in progress. The output from the middle node goes
ON when previously saved data has not been accessed using the LOAD
instruction. This prevents inadvertent overwriting of data in the SAVE buffer.
Top Node Content
The top node specifies a block of 4x registers to be saved to state RAM. The 4x
register entered here defines the beginning register of the block.
Middle Node Content
The middle node defines the specific buffer, within state RAM, where the block of
data is to be saved. Four 512 word buffers are allowed. Each buffer is defined by
placing its corresponding value in the middle node, that is, the value 1 represents
the first buffer, value 2 represents the second buffer and so on. The legal values
are 1, 2, 3, and 4. When the PLC is started all four buffers are zeroed. Therefore,
you may not SAVE data to the same buffer without first transferring data in the
buffer to 4x registers by using the LOAD instruction. When this is attempted the
middle output goes ON. In other words, once a buffer is used, it may not be used
again until the data has been removed.
Bottom Node Content
The bottom node contains the number of holding registers to be saved. The range
is 1 ... 512.
Start SAVE
operation
SAVE is active
4xxxx
1, 2, 3, 4
SAVE
#0512
SAVE not allowed