SNP Snapshot Function Block
(Pro version only, MBus_io12_LCD and MBus_io14_DIN devices only)

The Snapshot (SNP) function block adds a local history data capture facility for MBus_io12_LCD and MBus_io14_DIN devices. When triggered, the SNP block will capture the values of a defined list of parameters (values of other program blocks) and store those values along with a timestamp into flash memory. Subsequent triggers will add additional records overwriting older data in a circular fashion. The defined MBus_ioFlash program can contain many SNP blocks, each can have a different list of parameters and can be triggered independently. The output value of the block itself will be the number of records that have been captured so far.

An external device can read the captured data via standard Modbus "Read Holding Registers (03)" commands. Data values will be formatted as 16 bit signed integers, same format as is currently used to read block values via Modbus.

The memory storage space consumed by the SNP blocks is shared with the MBus_ioFlash program space which is limited to about 16000 bytes.  Each stored data record requires 6 bytes for the timestamp plus 2 bytes for each parameter. Hence the total memory consumption of one SNP block can be computed as: (6 + number_of_parameters * 2)* maximum_records. For example if a SNP block is defined with 15 parameters and a maximum of 52 records it will consume: (6 + 15 * 2) * 52 = 1872 bytes, which represents about 12% of the available program space.

SNP definition parameters

Parameter Description
Name Function block name, see common parameters
Modbus Reg no. The Modbus start register number to access the saved history data. The first register is the number of stored records and subsequent registers correspond to the stored data. The first 6 registers of each record is the time stamp, formatted as (year, month, day ,hour, minute, second), followed by the data.

Point list

The names of the blocks in the current MBus_ioFlash program page which will be acquired for each snapshot data record.

Max Records

Maximum number of snapshot data records to store. When exceeded, the oldest record is overwritten in a circular fashion.

Input Trigger

The input block that will trigger the storage of a new snapshot data record.
/ Mixed inputs option, see common parameters


Toggle button: specifies the type of trigger, low-to-high or high-to-low.