DESCRIPTION AND OPERATION
LOGIC POWER
2 - 4
WBPEEUI240754A0
®
Status Data
Status data consists of three separate 8-bit bytes read by the
control module. The first byte contains readback data that
reflects the state of the relays. The second byte is not significant,
it exists to have compatibility with the other DSO modules.
The third byte is the module identification and module status.
I/O module identification is in the four most significant bits
(MSB). It identifies the I/O module to the control module. It also
verifies the I/O expander bus communication integrity and the
control module configuration. I/O module status is the least
significant bit (LSB). During initialization, the control module
writes data to the output register and default register, and
forces this bit to a logic 1. A reset or
time-out
(bus fault error)
resets it to a logic 0. Default data is normally written only dur-
ing control module start-up. The control module reads the mod-
ule status bit to test for a change in the state of the module. It
uses this bit as a signal to rewrite data to the module to ensure
that proper default values are in the default register.
Output Data
Output data is one 8-bit byte sent to the output register. Each
bit of data represents one output. The bit value reflects the state
of the output. Logic 1 turns a field device ON; logic 0 turns it
OFF.
Default Data
Default data is one 8-bit byte sent to the default register. It is
set by the control module configuration (FC 128). The function
of this data is the same as the output data but is used only
when a
time-out
occurs.
LOGIC POWER
Logic power (+5 VDC) drives the DSO circuits. It connects
through the top 12-pin card edge connector (P1) shown in
Figure
RELAY POWER
Relay power (+24 VDC) drives the on-board relays. It connects
through the 30 pin card edge connector (P3) shown in Figure
2-1. The power line is protected against polarity inversion due
to a cabling error on the termination unit (TU) or termination
module (TM).
NOTE: Logic power ground and relay power ground are tied
together inside the module.
