Specifications

Command Set 4-12
The low limit value may be read back with the Read Low Limit (RL)
command. More information on alarms may be found in Chapter 6.
New Data Command (ND)
The New Data (ND) command is a variation of the Read Data (RD)
command used to read sensor data from the module. The ND command
guarantees that the output data has not been previously read.
The D1000 module acquires analog input data eight times a second and
stores the result in the output buffer (see Figure 2.1). The Read Data (RD)
command simply reads the results stored in the output buffer. A fast host
communicating at a high baud rate could possibly read the output buffer
several times before the information is updated with a new A/D conversion.
This results in redundant information which may be confusing or may be a
waste of host processor time.
Associated with the output buffer is the New Data Flag (see Figure 2.1). This
flag is cleared each time an RD or ND command is performed. The flag is
set when the module’s microprocessor loads the output buffer with the result
of the most recent A/D conversion. The ND command will output data only
when the New Data Flag is set. If the flag is cleared when an ND command
is received, the module will wait until new data is present in the output buffer
before responding to the command. Thus, the output data obtained with an
ND command is always the result of a new A/D conversion.
The ND command is especially useful with computers that handle commu-
nications on an interrupt basis. The ND command is used to get maximum
throughput without producing redundant data.
Command: $1ND
Response: *+00072.00
Command: #1ND
Response: *1ND+00072.009F
A special condition exists when using the ND command with the D1600
frequency/pulse modules. These modules differ from the other sensor input
modules in that they require an input trigger signal to obtain new data. If no
signal exists on the input of the D1600, an ND command will wait indefinitely
for new data and the module will not respond.
In order to escape this condition, a single control-C ($03) may be issued by
the host to abort the ND command. The aborted ND command will respond
with the data value currently stored in the output buffer. Be aware that on an
RS-485 system, the control-C character may interfere with the ND output
data, causing a communications collision.