This device driver is for Acromag IP231 8/16 channel DAC module and is
subclassed from asynPortDriver class written by Mark Rivers.
The carrier board and the daughter module are setup in st.cmd file in calls to

ipacAddXy9660("baseAddr,0")
carr1=ipacLatestCarrier()

drvIP231Configure("Port",carr1,slot,"modeString")

where baseAddr is a base address of the carrier board,
Port is an asyn port name,
carr1 is a value returned from the call to ipacLatestCarrier() function
      and is the carrier number (first carrier number is 0)
slot occupied by the daughter module (0 for A, 1 for B, etc)
ModeString is one of the {transparent,simultaneous}

When the device driver is configured, a software reset is issued to the module.
This sets output latches for all channels to 0V.  Then 0x8000 is written to all
input latches and 0V is also written to the ao records of all the channels,
and the operation mode is set to the value specified in the drvIP231Configure
command.

An EDM screen is provided which:
1. allows setting DAC output value for each channel,
2. shows the readback of the input latch for each channel,
3. allows to control the operating modes.

Note, that the input latch and the output latch, which is the actual value put
out by the DAC may not be the same if the operating mode simultaneous is
selected.  This module does not provide hardware for reading back the output
latches.

Also note that when the IOC using this module is first started, the output DAC
and the readback analog records both show the contents of the input latch
for each channel.  This assumes that the IOC is using the db files provided
with the driver support module.

Created on 3/12/2011 by zms