Status words – Rockwell Automation 1747-DCM,D17476.8 Direct Communication Module User Manual

Page 47

Chapter 6
Programming

6–5

The first word of the DCM I/O image is the status word. The status word
indicates the status of communication and data between the RIO scanner and
the DCM. Depending on what logical rack size the DCM is configured for, it
will transfer the following number of I/O words:

Rack Size

Number of RIO Words Transferred

Total Words

1/4 Logical Rack

One (plus one Status Word)

1/2 Logical Rack

Three (plus one Status Word)

3/4 Logical Rack

Five (plus one Status Word)

Full Logical Rack

Seven (plus one Status Word)

The figure below shows how I/O bits are transferred from the scanner to two
DCMs, each configured as a 1/2 logical rack device.

НН

Word 0

Word 1

Word 2

Word 3

Word 4

Word 5

Word 6

Word 7

DCM 1
1/2 Rack Device

НН

DCM 2
1/2 Rack Device

Status Word:

Data Words:

R = Reserved for future use

Bit Number: Decimal

RIO Scanner Input Status Word Examination (Decimal)

This is the input status word sent in a data transfer from a supervisory
processor/RIO scanner to a DCM. These bits can be used as conditional
logic in your SLC program to flag DCM, RIO, or supervisory processor
system errors and/or status. Scanner status bits not defined below are
reserved for future use.

DCM Initialization bit. This bit is set when the DCM is in its power-up initialization.
It will be cleared when valid data is received from the supervisory processor output
image table.

ЙЙ

ЙЙЙ

ЙЙ

ЙЙЙ

ЙЙ

ЙЙЙ

ЙЙ

ЙЙЙ

ЙЙ

ЙЙЙ

Program/Test/Fault Mode bit. This bit is set whenever the
supervisory processor is in the Program, Test, or Fault Mode.

ЙЙ

Logical OR of other Status Word bits. It is set when any
other bit is set. It is cleared when all other bits are cleared.

Communication Error bit. This bit is set whenever the DCM detects an RIO communication
error. It is cleared when the Communication error is cleared.

Reserved Bits

НН

DCM

ЙЙ

Status Bits

Status Words