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3 PROTOCOL IMPLEMENTATION
3.1 ASCII Specific and Direct Requests
The ASCII protocol implements two different types of messages to transfer data between a master application
and the instrument: specific requests and direct read/write requests.
Specific ASCII requests use different formats for accessing different data locations. The message body differs
depending on the request type. Each data field has a fixed position in the ASCII string. Chapter 4 describes
specific ASCII requests and their message body formats.
Direct read/write requests use a universal message body format, specified in Section 5.1. These requests allow a
master application to access different data locations (registers) in the instrument by specifying a direct register
index. A number of consequent registers can be read or written by a single request by specifying an arbitrary start
register and the number of registers to be accessed. Chapter 5 describes registers accessed via direct read/write
requests and their contents.
All measurement data in your instrument can be accessed using direct read requests, and some data can be read
via specific ASCII requests. In all cases, a direct register read offers you more precise data with extended
resolution. Setup data can be partially accessed using both specific and direct requests, and partially via either
specific or direct requests.
3.2 Data Formats
Specific ASCII requests use both decimal and hexadecimal notation. Direct requests transfer ASCII data only in a
hexadecimal notation.
Using a decimal notation, data is transmitted in a decimal representation as is, i.e., no conversion is needed.
Negative numbers are transmitted with a sign at the left. Fractional numbers are represented with a decimal point.
When the value exceeds the field range, it is truncated to the right.
In a hexadecimal notation, each data byte is transferred by two hexadecimal characters in ASCII representation
(i.e., ASCII printable characters 0-9, A-F are used to represent hexadecimal digits 0h-9h, 0ah-0fh). All data is
transferred as 2-character (8-bit unsigned byte), 4-character (16-bit unsigned or signed integer) or 8-character
(32-bit unsigned or signed long integer) whole numbers. Negative numbers are transmitted in 2-complement
code. Each data byte is transmitted high order digit first. Each integer or long integer register is transmitted high
order bytes first.
Fractional numbers are transmitted being scaled by 10 in power N, where N is the number of digits in the
fractional part. For example, the frequency reading of 50.01 Hz is transmitted as 5001 being pre-multiplied by
100. Whenever a data register contains a fractional number, the register measurement unit is given with a
multiplier ×0.1, ×0.01 or ×0.001, showing an actual register resolution (the weight of the least significant decimal
digit). To get an actual fractional number with specified precision, scale the register value with the given multiplier.
To write a fractional number into the register, divide the number by the given multiplier.
3.3 Configuring and Accessing Log Files
Configuring Memory for Logging
To use the onboard data logging, allocate a separate log partition for each specific data you want to be recorded
in your instrument. The PM172EH provides concurrent recording data in 11 different memory partitions, one of
which is intended to record event log data, two - for waveform recording, and the others to store 8 different data
logs using different sets of data parameters. Additionally, the two last data logs #7 and #8 can be configured to
automatically record TOU monthly and daily profile data respectively using season TOU tariffs. Refer to Section
4.15 for information on how to allocate a memory partition for your specific data. Refer to Section 4.16 on how to
configure a set of parameters to be recorded to each data log.
Each memory partition you allocated for logging is organized as a sequential file of records where all data is
recorded in chronological order with a time and date stamp. When a partition is filled up, recording can be
stopped or can continue to record over the oldest records if you specified a partition with a wrap-around (circular)
attribute. TOU profile log partitions are automatically configured to be of a wrap-around type.
Each record within a log file has a unique sequence number that guards against missing or duplicated records
when reading the log file. This number is incremented (modulo 65536) with each log and will not be replicated
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