DESCRIPTION AND OPERATION
MODULE DATA
I-E96-310B
2 - 5
MODULE DATA
Function code 83 in the control module configuration accesses
the DSO module on the I/O expander bus. It also allows the
control module to automatically read status data from the I/O
module, and write output data to it. The I/O module address in
function code 83 must be the same as the address set on the
I/O expander bus address dipswitch (dipswitch S1).
Status Data
Status data consists of three eight-bit bytes read by the control
module. The first byte contains readback data that reflects the
state of the solid state output relays. Each bit of this data cor-
responds to the digital output state (on or off). The second byte
is the fuse status; each bit reflects the condition of a fuse (logic
one = blown fuse, logic zero = good fuse). The third byte is the
module identification and module status. I/O module identifi-
cation 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 one. A reset or time-out condition (bus fault error) resets
it to a logic zero. Default data is normally written only during
control module start-up. The control module reads the module
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 insure that
proper default values are in the default register. A fuse LED
status bit reflects the state of the LED: logic one (on), logic zero
(off).
Output Data
Output data is an eight-bit byte sent to the output registers.
Each bit of the digital output byte corresponds to one output.
The bit value reflects the state of the output. Logic one turns a
field device on; logic zero turns it off.
Default Data
Default data is an eight-bit byte sent to the default registers. It
is set by the control module configuration (function code 128).
The function of this data is the same as the output data but is
used only when a time-out condition occurs.
LOGIC POWER
Logic power (+5 VDC) drives the DSO module circuits. It con-
nects through edge connector P1 shown in Figure
.
