Campbell CR6 Series, Operator'S Manual

Page: 367 / 690

Section 7. Installation
367
non-zero, then SerialInRecord() allocates only this many bytes instead of
the number of bytes specified by SerialOpen() ).
• Variable Declarations — Variables used to receive data from the serial
buffer can be declared as Public or Dim . Declaring variables as Dim
has the effect of consuming less comms bandwidth. When public
variables are viewed in software, the entire Public table is transferred at
the update interval. If the Public table is large, comms bandwidth can
be taxed such that other data tables are not collected.
•
String Declarations
— String variables are memory intensive.
Determine how large strings are and declare variables just large enough
to hold the string. If the sensor sends multiple strings at once, consider
declaring a single string variable and read incoming strings one at a time.
The CR6 adjusts upward the declared size of strings. One byte is always
added to the declared length, which is then increased by up to another three
bytes to make the length divisible by four.
Declared string length, not number of characters, determines the memory
consumed when strings are written to memory. Consequently, large strings
not filled with characters waste significant memory.
7.7.18.5.6 Serial I/O Example I
CRBasic example Receiving an RS-232 String
(p. 367)
is provided as an exercise in
serial input / output programming. The example only requires the CR6 and a
single-wire jumper between
COM1 Tx
and
COM2 Rx
. The program simulates a
temperature and relative humidity sensor transmitting RS-232 (simulated data
comes out of COM1 as an alpha-numeric string).
Receiving an RS-232 String
'This program example demonstrates CR6 serial I/O features by:
' 1. Simulating a serial sensor
' 2. Transmitting a serial string via COM1 TX.
'The serial string is received at COM2 RX via jumper wire. Simulated
'air temperature = 27.435 F, relative humidity = 56.789 %.
'Wiring:
'COM1 TX (C1) ----- COM2 RX (C4)
'Serial Out Declarations
Public TempOut As Float
Public RhOut As Float
'Declare a string variable large enough to hold the output string.
Public SerialOutString As String * 25