905U-G Wireless Gateway
User Manual
Page 71
©September 2004
Discrete I/O
The value of a digital I/O point is stored in the 905G database as a hexadecimal '0000' (“off”) or
hex 'FFFF' (“on”). However the 905G will generate either a ‘0’ (“off”) or ‘1’ (“on”) to a binary
file when initiating a “Typed Logical Write” command or responding to a “Typed Logical Read”
command. Similarly, the 905G will accept ‘0’ or ‘1’ from responding device to a “Typed
Logical Read” command or from an initiating device generating a “Typed Logical Write”
command and store ‘0000’ or ‘FFFF’ in the database location. The file type for a binary file (bit
file) is 0x85.
In the PLC (that is, the DF1 host device), discrete values (“bits”) are stored in 16 bit registers -
each register stores 16 bit values (or 16 discrete values). You can only transfer these values in
groups of 16. That is, a read or write command will transfer a minimum of 16 bits to/from the
905G. If more than 16 are transferred, then they will be transferred in multiples of 16. You
cannot transfer an individual bit - you must transfer the 16 bits in that PLC register, which will
be transferred to/from 16 consecutive I/O registers in the 905G.
Note: The PLC reads or writes digital bits starting at the LSB of each register. In the 905G,
only one bit is written to each I/O register, and this is the MSB.
Analog I/O
Analog I/O from the remote 905U modules are 16 bit register value. A value of 8192 (hex 2000)
represents 0mA. A value of 49152 (hex C000) represents 20mA. Each mA has value of 2048
(hex 0800) - a change of 4096 (hex 1000) is equivalent to a change of 2mA. A 4-20mA signal
will vary between 16384 (hex 4000) and 49152 (hex C000). A 0-20mA signal will vary between
8192 (hex 2000) and 49152 (hex C000).
Note:
If analog values are read to and written from an integer file in an SLC or Micrologix CPU,
integer files contain 16 bit
signed
values. These represent values in the range -32768 to 32767.
The data values from the 905U modules are treated as 16 bit
unsigned
values. To convert the
data from an analog input, move the data from the integer file to a long file (MOV command)
