Spectrum Controls 1769sc-HART Modules - Manual (Page 64)

Compact IO™ Isolated HART Analog Output Module
User’s Manual 0300217-03 Rev. A
6-12
Note: It is up to the user to keep the unlatch bit set until verification that the process
alarm bit has cleared. When the process alarm bit has cleared the user can then clear
the unlatch process alarm bit.
Note: The module will not latch the high process alarm if a transition from “no alarm
condition” to “alarm condition” occurs while the unlatch high process alarm bit is set.
6.4.3 Unlatch Process Low Alarms UL0 to UL3 (Word 4)
UL0 through UL3 will unlatch the low process alarms for channels 0 through 3
respectively. Refer to section 6.3.12 for more information regarding setting the alarm
latch function. To unlatch the low process alarm on a given channel, set the associated
unlatch alarm bit to 1.
Note: Setting the unlatch process alarm bit will not clear the alarm latch if the
conditions that generated the alarm are still present.
Note: It is up to the user to keep the unlatch bit set until verification that the process
alarm bit has cleared. When the process alarm bit has cleared the user can then clear
the unlatch process alarm bit.
Note: The module will not latch the low process alarm if a transition from “no alarm
condition” to “alarm condition” occurs while the unlatch low process alarm bit is set.
6.4.4 Hart Suspend HS0 to HS3 (Word 4)
HS0 to HS3 are used to suspend all HART acquisition, except Pass-through messages, on
channels 0 through 3 respectively. To suspend HART acquisition, set the associated
channel suspend bit to 1. Normal HART acquisition will resume when the bit is cleared.
Note: A channel that is placed out-of-service (i.e. Suspended) will automatically
resume service after three minutes, as long as no pass-through commands are issued
before the three minutes expires.
6.4.5 Packet Just Scanned (Word 5)
When demultiplexing HART data from the module, this output word can be used to
speed up the acquisition process by overriding the automatic 500ms acquisition delay
between packets.
1
To override the delay, the packet just scanned word needs to be
populated with word six from the input data file on each scan of the ladder program.
Input word six contains the channel and packet number just scanned.
Note: Input word six is the first word of twenty which contains the multiplexed HART
data for each channel.
6.4.6 Message Master Control (Word 6)
This word is used to control the data flow of a message sent to the module. These
messages include module commands such as HART pass-through, HART suspend and
resume, and get device information.
1
6.4.7 Message Request Size (Word 7)
The message request size determines the size of the message, in bytes, that will be sent to
the module.
1
6.4.8 Message Request Buffer (Words 8…27)
The message request buffer contains the data making up the message that will be sent to
the module.
1
1 Refer to Chapter 7 for more details.