Appendix F: PMS Multi-Drop Protocol (MiniLaz Emulation)
Page F-2
Lasair II Particle Counter Operations Manual
The Lasair II particle counter provides an extended version of the command set
used in the obsolete MiniLaz instrument, and offers backward compatibility. This
protocol allows a Lasair II particle counter to be a drop-in replacement for a
MiniLaz on a Facility-View installation.
Multi-Drop Command Coding Overview
Commands in the PMS protocol are formatted in the following manner. For users
wishing to write their own drivers, basic communication routines are available from
Particle Measuring Systems.
Formatting Command Codes
To properly format a command code:
1
Add the address of the instrument to the beginning of the command string. The
address is an unsigned 16 bit integer between 0 and 99.
2
Add a 16 bit checksum of the data and address to the end of the packet. The
checksum is an unsigned sum of every address and data byte.
At this point the packet should look like this:
ADDR_HIGH_BYTE | ADDR_LOW_BYTE | DATA_1 | DATA_2 | ... | DATA_N |
CHECKSUM_HIGH_BYTE | CHECKSUM_LOW_BYTE
3
ASCII characters not in the range of 0x20 to 0x7E must be converted to a 2-byte
sequence using the following table:
4
Pre-append an ASCII <STX> character (0x02) to the data stream, and post-
append an ASCII <ETX> character (0x03) to the data stream.
5
Data is ready to transmit.
ORIGINAL BYTE
TRANSMITTED BYTES
byte < 0x20
0x7B, byte+0x20
0x7B <= byte < 0x80
0x7C, byte-0x5B
0x80 <= byte < 0xC0
0x7D, byte-0x60
0xC0 <= byte
0x7E, byte-0xA0
