IOtech MultiScan 1200, User Manual

Page: 207 / 364

TempScan / MultiScan User's Manual Chapter 13: System Operation 197
System Operation 13
Acquisition Buffer……197
Buffer Organization……198
Buffer Query Operation……199
Buffer Read Operations……201
Buffer Overrun……207
High/Low/Last (HLL) Registers……209
Contents of the HLL Registers……209
Access to the HLL Registers……209
Comparing Buffered Data to HLL Data……214
Status-Reporting & Mask Registers……214
Theory of Operation……215
Status-Reporting Registers……216
Mask Registers……220
Using Status-Reporting Registers……220
Additional Operation……222
Trigger Latency……222
Real-Time Clock……222
Open Thermocouple & Range Error Checking……223
Software Digital Filtering (TempScan/1100 Only)……223
Acquisition Buffer
The TempScan/1100 or MultiScan/1200 Acquisition Buffer is a FIFO (First-In First-Out) buffer. In
other words, the oldest scan data to be written into the buffer is the first scan data to be read from the
buffer when a read operation is performed. Then once the scan data is read from the buffer by the
controller, that data is erased from the buffer.
The buffer may consist of one or more Trigger Blocks . In turn, a Trigger Block can consist of the
following components as discussed in the previous chapter: Pre-Trigger scans (optional), Post-Trigger
scans (required), and Post-Stop scans (optional). These components constitute a single Trigger Block
in the internal memory of the TempScan/1100 or MultiScan/1200 unit. Each Trigger Block defines an
acquisition and thus contains one and only one Trigger (trigger start event). These Trigger Blocks may
also be variable in length.
Multiple Trigger Blocks are allocated sequentially, and the scans within each Trigger Block are written
and read sequentially. It is not possible to randomly access a Trigger Block or a scan within a Trigger
Block . When a read operation is performed, the scan that is read is the oldest scan in the oldest trigger
block currently defined.