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5
.
2
.
6
Command Register (base + 7)
The command register is used for sending control commands to the DAQP card including
arm/trigger (or start A/D), scan list queue and data FIFO flush, stop A/D and timer/counter
latch commands. It also sets the data program/access mode for the data FIFO. The command
bits (bit 3 to 7) are actually ‘monostable’ or self-clearing after the specified command function
is completed and do not require clearing. Although it is possible, sending multiple
commands in one I/O instruction is not recommended.
The data FIFO program/access bit and the scan speed selection bits are latched each time they
are written. The user must avoid changing these bits accidentally when sending the
commands to the DAQP series cards. Bit definition is shown in Table 5-16.
Table 5-16. Command Register Bit Definition
1 = data access, 0 = program thresholdData FIFO program/access0
00 = 100, 01 = 50, 10 = 25 (kHz)Scan rate selection2-1
1 = latch, 0 = no action
Latch timer/counter command
3
1 = stop, 0 = no actionStop A/D command4
1 = flush, 0 = no actionFlush scan list command5
1 = flush, 0 = no action
Flush data FIFO command
6
1 = send trigger/arm, 0 = no actionTrigger/Arm command7
ExplanationFunctionBit
5.2.6.1 Trigger/Arm Command
If the trigger source is internal (software trigger), writing a “1” to bit 7 will send a trigger to the
DAQP card and start the A/D conversion process. If the trigger source is external (TTL or
analog), writing a “1” to bit 7 will serve as the arm command. The arm command tells the
DAQP card to look for the specified external trigger edge from the moment the command is
received. Never issue the arm command and the A/D stop command simultaneously. The
arm command initiates data acquisition and the A/D stop command terminates it.
5.2.6.2 Flush Scan List Queue Command
The scan list queue must be flushed before it can be programmed. This command should be
issued before the flush data FIFO command. The queue may have up to 2048 word entries,
each containing two bytes. It is the user’s responsibility to guarantee the integrity of the
entries.
DAQP-208/208H/308 Users Manual 51