Rockwell Automation 1771-DCM User Manual

AllenBradley

Direct
Communication

User

Module

(Cat. No. 1771-DCM)

Manual

Table of Contents

To Our Customers 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

To Our Customers 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manual's Purpose 11
Intended Audience 11
Terminology 11
Related

Publications

Overview of Direct Communication Module 21. . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Overview
Describing the 1771DCM 21
Choosing 1771DCM or Data Highway 22
Selecting
Example
Compatible Processors 23
Keying 23

of Direct Communication Module

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .

Options

Applications

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21. . . . . . . . . . . . . . . . . .

22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Selecting Options 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Selecting
Switch Bank 0 32
Switch Bank 1 34

Options

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Connecting Cables 41. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Connecting Cables 41. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Module Connector 41
Daisy Chain Hookup 42
Trunkline/Dropline Hookup 43

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the Status Word 51. . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the Status Word 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Examining
Status Bits Read by the Local Processor 52
Status Bits Read by the Supervisory Processor 53

Status Bits

51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

Programming the 1771-DCM 61. . . . . . . . . . . . . . . . . . . . . . .

Programming the 1771-DCM 61. . . . . . . . . . . . . . . . . . . . . . . . . . .

Local Processor Logic 61
1771-DCM
Supervisory Processor Logic 63
Processor/Module

Switch Settings

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . .

Compatibility

63. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

613. . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contentsii

Calculating Transfer Time 71. . . . . . . . . . . . . . . . . . . . . . . . .

Calculating Transfer Time 71. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Discrete Transfer Time 71
Block Transfer Time 74
Block Transfer with a PLC3 Supervisory Processor 76

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . .

Troubleshooting Your 1771-DCM 81. . . . . . . . . . . . . . . . . . . .

Troubleshooting Your 1771-DCM 81. . . . . . . . . . . . . . . . . . . . . . . .

LED Display for Normal Operation 81
LED

Display for Fault Conditions
Causes of Block Transfer Errors 82
Errors

Indicated by Status Bits

Specifications 84

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . .

81. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

83. . . . . . . . . . . . . . . . . . . . . . . . . .

To Our Customers

Chapter

1

To Our Customers

Manual's Purpose

Intended Audience

The following information may be helpful when using this manual:

The purpose of this manual is to help you understand the intended
application of your Direct Communication Module (cat. no.
1771-DCM) and operate your 1771-DCM correctly in the shortest
possible time. We show you how to:

Select Module Options to Fit your Application Chapter 3
Install and Connect Your 1771-DCM Chapter 4
Use Status Bits to Detect Faults Chapter 5
Program the Transfer of Data between Processors Chapter 6
Compute the Transfer Time between Processors Chapter 7
Troubleshoot Module or System Malfunctions Chapter 8

We assume you are familiar with installing and using Allen-Bradley
programmable controllers and that you have written ladder diagram
programs. If not, we suggest that you study the Programming and
Operations Manual of your processor(s) listed below under Related
Publications.

Terminology

Related Publications

We have written this manual using current programmable controller
terminology and have attempted to keep it free of jargon. If you
encounter terms that you do not understand, we suggest that you obtain
the current booklet, Programmable Controller Terms, listed below under
Related Publications.

You should be able to install and operate your 1771-DCM without the
need for additional publications. If not, the following publications may be
of interest to you:

11

Chapter 1

To Our Customers

Title Publication

1771ASB

Programmable Controller T

PLC2/05 Programming Manual

PLC2/15 Programming Manual

PLC2/02, 2/16, 2/17 User's Manual

PLC2/30 Programming Manual

PLC3 Programming Manual

PLC5 Family Processor Manual

PLC5/250 Programmer's Manual

Remote I/O Adapter

erms PCGI7.2

17716.5.37

17726.8.6

17726.8.2

17726.5.8

17726.8.3

17756.4.1

17856.8.2

50006.4.1

12

Chapter

2

Overview of Direct Communication Module

Overview of Direct
Communication Module

Describing the 1771DCM

Local
Proc.

PLC-2
PLC-5

Allen-Bradley has introduced the Direct Communication Module (cat. no.
1771-DCM) to meet the growing need for communication between PC
processors.

The 1771-DCM is a chassis-mounted single-slot I/O module that allows
communication between a supervisory processor and local processors
(Figure 2.1). The local processor can be chassis-mounted or configured
as a local or remote system.

Figure 2.1

and Remote Configurations

Local

Local Configuration

Bidirectional

Block Transfer

S
C

D
C

M

A
N
N
E
R

Supervisory

Processor

PLC–2/30
PLC–3 Family
PLC–5/15
PLC–5/25
PLC–5/250

Local

Processor

PLC–2/30
PLC–3 Family
PLC–5/250

S
C
A
N

N
E
R

Remote I/O Link

1771–ASB Protocol

1
7
7
1

­A

S

Remote I/O Link

1771–ASB Protocol

Remote Configuration

Bidirectional

Block Transfer

D
C

M

Remote I/O Link

1771–ASB Protocol

S
C
A
N

N
E
R

Supervisory

Processor

PLC–2/30
PLC–3 Family
PLC–5/15
PLC–5/25
PLC–5/250

12825

21

Chapter 2

Overview of Direct
Communication Module

The 1771-DCM passes data table values such as command bits, status
bits, and data blocks between supervisory and local processors. The
supervisory processor typically writes commands and/or data table values
to the local processor, and reads resulting status, diagnostic data, and data
values from the local processor (or vice versa).

The supervisory processor communicates serially with the 1771-DCM as
though it were a 1771-ASB Adapter Module, and addresses the
1771-DCM as though it were addressing a separate I/O chassis. You
select the mode of transfer between the supervisory processor and
1771-DCM: discrete transfer (up to eight words) or block transfer (up to
64 words). Either mode includes one status word.

The local processor communicates with the 1771-DCM over the
backplane using block transfers and addresses the 1771-DCM as an
intelligent I/O module. When the local processor is remotely configured,
it communicates with the 1771-DCM via block transfer through its
scanner-adapter link.

Choosing 1771DCM or Data
Highway

Selecting Options

The 1771-DCM and data highway allow communication between PC
processors. Consider the following factors when determining the
appropriate choice. Use the 1771-DCM to:

Transfer data table words
Obtain predictable transfer times
Transfer up to eight words when transfer time over a remote I/O

channel is adequate, in addition to the transfer time of the local
processor and 1771-DCM

Transfer up to 64 words when transfer time for block transfers over a

remote I/O channel is adequate, in addition to the transfer time of the
local processor and 1771-DCM

Decrease data highway traffic

At least one processor must have a remote I/O scanner.

You cannot transfer ladder diagram programs nor messages stored in the
message area of memory using the 1771-DCM.

You can select one or more of the following options depending on your
application requirements using switches on the module:

22

Chapter 2

Overview of Direct
Communication Module

Baud

Rate/Distance

T

ransfer Method

Rack Size

Protected Data

I/O Rack Address Designate the I/O rack number, the number of the first module group

Select the communication rate and distance to the supervisory proces
sor as either 57.6K baud to a distance of 10,000 feet, or 1
to a distance of 5,000 feet.

Select block transfer or discrete data transfer between the 1771DCM
and the supervisory processor

When using discrete data transfer
termines how the 1771DCM appears to the scanner of the superviso
ry processor (the size of the I/O chassis simulated by the 1771DCM).
This also determines the number of words transferred.

Select protected data to prevent block transfers from the local proces
sor until the supervisory processor has received the previous block
transfer.

of the I/O chassis simulated by the 1771DCM, and whether it has the
highest starting module group address of two or more chassis as
signed to the same rack address.

.

, select the number of slots that de

15.2K baud











Example Applications

Compatible Processors

Keying

These options are described in Chapter 3.

You can use the 1771-DCM in a variety of applications where the transfer
of data table values is required. For example, consider using it to:

Call messages stored in the data table of the supervisory processor and

outputted through an ASCII I/O module (cat. no. 1771-DA) or BASIC
module (cat. no. 1771-DB)

Download recipe data table values from supervisory to local

processor(s) where you want local processor(s) to execute different
versions of the same program

Download commands from the supervisory processor to execute

different sections of a ladder diagram program at the local processor

Use the 1771-DCM with any Allen-Bradley programmable controller that
uses block transfer and the 1771 I/O structure.

Reserve an I/O slot for this module by placing keying bands on the
backplane connector. Position keying bands between the following
numbers labeled on the backplane adjacent to the upper backplane
connector. The keying bands mate with corresponding slots in the module
connector:

Between 2 and 4
Between 16 and 18

23

Selecting Options

Chapter

3

Selecting Options

Select one or more of the following options depending on your
application requirements. Do this by setting switches in Switch Banks 0
and 1 on the left (metal cover) side of the 1771-DCM. To assist you, we
have printed a table of switch settings for each switch bank on the
module’s cover next to the switches (Figure 3.1).

Figure 3.1
Tables

for Switch Settings

BANK 0

SW SW SW SW SW SW SWITCH

BAUD

RATE

57.6

115.2

I/O RACK

NUMBER

1

P

P

2

L

L

3

C

C

4

-

_

5

5

6

2

7

&

5
/
2
5
0

P
L
C
_

3

NOTE: DO NOT USE OTHER SWITCH POSITIONS

LAST

RACK

12 3 45 6 78

Not

NO

Used

YES

12 34 5 6

00

01
02
03
04
05
06
07
10
11
12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

TRAN S

MTHD

BLOCK
DSCRT

BANK 1

SWITCH SWITCH

DATA

PTCT

Not

NO

Used

YES

FIRST

MODULE

GROUP NO.

0
2
4
6

ON

CLOSED

OFF

OPEN

RACK

SIZE

1/4
1/2
3/4

FULL

78

1

B

2

A

3

N

4

K

5
6

0

7
8

1

B

2

A

3

N

4

K

5
6

1

7
8

17906

31

Chapter 3

Selecting Options

Each switch bank has eight switches. Set each switch to the ON (closed)
position by depressing the right-hand side of the switch or to the OFF
(open) position by depressing the left-hand side of the switch (Figure 3.2).

Figure 3.2
Example

Switch Bank

OPEN

1

2 3 4 5 6 7 8

Switches 1 and 3 are OFF (open)
Shading represents the switch position

Switch Bank 0

12826

The options that you select with Switch Bank 0 are as follows:

Switch 1  Baud Rate

ON (Closed) for 57.6K Baud
OFF (Open) for 115.2K Baud

Set the baud rate equal to that of the scanner of your supervisory
processor. You can transmit data up to 10,000 feet at a data rate of

57.6K baud or up to 5,000 feet at a data rate of 115.2K baud.

Switch 2  Not Used

32

Chapter 3

Selecting Options

Switch 3  Last Rack

ON (Closed) Not Last Rack
OFF (Open) Last Rack

If the 1771-DCM is assigned the same I/O rack number as other I/O
chassis, designate whether this I/O chassis is the last chassis (has the
highest starting module group number) of those assigned the same rack
number. (Refer to I/O Rack Number below.)

Switch 4  Transfer Method

ON (Closed) for Block Transfer
OFF (Open) for Discrete Data Transfer

Choose either discrete data transfer or block transfer between the
supervisory processor and 1771-DCM. With discrete transfer, the rack
size you select determines the number of words transferred as either 2, 4,
6, or 8 words including a status word. Data is transferred between the
1771-DCM and the supervisory processor as serial remote I/O data for
each slot of the simulated I/O chassis. The supervisory processor updates
the 1771-DCM as if it were an I/O chassis on a remote I/O link.

With block transfer, you can transfer up to 64 words including a status
word. The 1771-DCM appears to the supervisory processor as a remote
1/4 rack. Data is transferred between the first I/O slot simulated by the
1771-DCM and the supervisory processor when the supervisory
processor’s ladder program executes block transfers.

Communication between the 1771-DCM and local processor is always
block transfer regardless of the mode of communication between
1771-DCM and supervisory processor.

Switch 5  Not Used

Switch 6  Protected Data

ON (Closed) for Unprotected Data
OFF (Open) for Protected Data

This option maintains data integrity and maintains the order of data blocks
sent from the local processor to the supervisory processor only when you
select block transfer. The 1771-DCM does not recognize the start of a

33

Chapter 3

Selecting Options

new write block transfer from the local processor until the supervisory
processor has read the previous data from the 1771-DCM.

When you select unprotected data, the local processor updates the
1771-DCM continually, regardless of whether the supervisory processor
has read the data from the 1771-DCM.

Switches 7 and 8  Rack Size

Switch

7

ON ON 1/4

ON OFF 1/2

OFF ON 3/4

Switch 8

Rack Size

Switch Bank 1

OFF OFF Full

When your application requires the transmission of discrete data words,
the 1771-DCM appears to the scanner of the supervisory processor as a
4-, 8-, 12-, or 16-slot remote I/O chassis for the transfer of either 2, 4, 6,
or 8 words respectively. Select the equivalent rack size depending on the
number of words of discrete data you want to write or read. One slot is
equivalent to eight discrete data bits. One module group is equivalent to a
word. A full rack is equivalent to eight data words. The 1771-DCM
inserts one status word in the transfer regardless of the equivalent rack
size you select.

When you set the 1771-DCM for block transfer, the 1771-DCM appears
to the scanner of the supervisory processor as a block transfer module in
the first module group of a four-slot chassis (1/4 rack). You can read and
write up to 64 words including one status word. Slots 1 through 3 are not
used.

The options that you select with Switch Bank 1 are as follows:

34

Switches 1 through 6  I/O Rack Number

PLC2

Family

1  7

PLC3 and PLC5/250

0 thru 37 octal

PLC5/15 PLC5/25

1  3 1  7

Chapter 3

Selecting Options

Designate the I/O rack number that you assign to the 1771-DCM with
Switches 1 - 6 of Switch Bank 1 (Table 3.A).

Table 3.A

Rack Number Selection for PLC2, PLC3, and PLC5 Family Processors

I/O

Switch

I/O Rack Number (Octal)

1 0 ON ON ON ON ON ON

P 2 1 ONON ON ON ON OFF

L 3 2 ONON ON ON OFF ON

C 4 3 ONON ON ON OFF OFF

5 4 ONON ON OFF ON ON

2 6 5 ONON ON OFF ON OFF

7 6 ONON ON OFF OFF ON

PLC-3
&
PLC5/250

PLC­5/15

7 ON ON ON OFF OFF OFF

10 ON ON OFF ON ON ON

11 ON ON OFF ON ON OFF

12 ON ON OFF ON OFF ON

13 ON ON OFF ON OFF OFF

14 ON ON OFF OFF ON ON

15 ON ON OFF OFF ON OFF

16 ON ON OFF OFF OFF ON

17 ON ON OFF OFF OFF OFF

20 ON OFF ON ON ON ON

21 ON OFF ON ON ON OFF

22 ON OFF ON ON OFF ON

23 ON OFF ON ON OFF OFF

24 ON OFF ON OFF ON ON

25 ON OFF ON OFF ON OFF

26 ON OFF ON OFF OFF ON

27 ON OFF ON OFF OFF OFF

1 2 3 4 5 6

PLC­5/25

35

Chapter 3

Selecting Options

Switch

I/O Rack Number (Octal)

30 ON OFF OFF ON ON ON

31 ON OFF OFF ON ON OFF

32 ON OFF OFF ON OFF ON

33 ON OFF OFF ON OFF OFF

34 ON OFF OFF OFF ON ON

35 ON OFF OFF OFF ON OFF

36 ON OFF OFF OFF OFF ON

37 ON OFF OFF OFF OFF OFF

1 2 3 4 5 6

Switches 7 and 8  First (Starting) Module Group Number

First

Module

Group Number

0 ON ON

2 ON OFF

4 ON ON

6 OFF OFF

7 8

Switch

Assign a unique stating module group number--such as 0, 2, 4, or 6--in
accordance with the number of chassis you assigned to the same I/O rack
number. You can assign from one to four 1771-DCMs and I/O adapters to
the same I/O rack number, provided that the combination does not exceed
a full rack. For example, assign starting module group numbers to each
I/O chassis or 1771-DCM in the following combinations:

Rack

Configuration

•

Four 1/4 Racks

• T

wo 1/2 Racks

•

One 1/4 and One 3/4 Rack

•

One 3/4 and One 1/4 Rack

Assign Module Group Numbers

0, 2, 4, and 6

0 and 4

0 and 2

0 and 6

36

You selected the equivalent rack size of your 1771-DCM with Switch
Bank 0, Switches 7 and 8, above.

Connecting Cables

Chapter

4

Connecting Cables

Module Connector

The communications channel between the 1771–DCM and a supervisory
processor is the same serial communications channel as used between the
1771–ASB Remote I/O Adapter (Series A) and the scanner of a
supervisory processor. You insert the 1771–DCM in a local or remote I/O
chassis and configure the 1771–DCM as an I/O chassis unique to the
supervisory processor. You can connect the 1771–DCM in a daisy chain
or trunkline/dropline hookup with other remote I/O chassis.

Make your connections to the connector at the bottom of the module
(Figure 4.1). Connector terminals are labeled at the bottom of the left
cover plate. Connector terminals accommodate two cables––one for the
incoming line of a daisy chain hookup, the other for the outgoing line.
Use either set of connector terminals for the dropline in the
trunkline/dropline hookup. Terminal 1 is connected to Terminal 4,
Terminal 2 to Terminal 5, and Terminal 3 to Terminal 6 inside the
1771–DCM.

WARNING: Do not disconnect this connector in a daisy chain
hookup when the system is operating because you disconnect
the remaining I/O chassis in the daisy chain. The connection
between terminals is inside the 1771–DCM.

Figure 4.1
Cable

Connections

Line 2

Shield

Line 1

Line 2

Shield

Line 1

Connector on 1771-DCM

(Clear)

(Blue)

(Clear)

(Blue)

Mating Connector

1

I/O Cable

Install a 150 ohm 1/2 watt resistor when the 1771-DCM

1

is simulating the last I/O chassis in the daisy chain.

12827

41

Chapter 4

Connecting Cables

Daisy Chain Hookup

When using the daisy chain hookup (Figure 4.2), splice each I/O chassis
into the main communication line (serial I/O channel). Install a 150 ohm
terminator resistor between the terminals of Lines 1 and 2 at the scanner
and at the last hookup on the main communications line to terminate both
ends of the line.

Figure 4.2
Example

PLC -2/ 30

Daisy Chain Hookup

1772 - SD2

1

Blue

1

Shield

Clear

2

Blue
Shield
Clear

Blue

1

Shie ld

2

Clear

3

1771 - ASB

Clear

Shie ld

Blue

2

1

2

1

1771 - DCM

Cle ar
Shield

Blue

1771 - ASB

Remote I/O Chassis

1771 - ASB

1

Install Terminator Resistor:
150oh m 1/2 watt

1771 - DCM

12661

42

Chapter 4

Connecting Cables

Trunkline/Dropline Hookup

PLC -2/30

When using the trunkline/dropline hookup, connect the 1771–DCM to the
serial I/O channel trunkline using a dropline that does not exceed 100 feet
in length (Figure 4.3). Connect the dropline to the trunkline using a T
connector (cat. no. 1770–XG) or a station connector (cat. no. 1770–SC).
There are no restrictions as to the spacing between station connectors or T
connectors if you do not exceed the maximum cable distance. Terminate
the open port at the first and last T connector or station connector using a
Terminator Set (cat. no. 1770–XF).

Figure 4.3
Example

Trunkline/Dropline Hookup with T Connectors

Blue

1772 - SD2

1

2

Shie l d

Clear

1771 - ASB

Bl ue
Shield
Clear

1
2
3

1771 - ASB

2

1

2

1

1771 - DCM

Cle ar

Shield

Blue

1

Remote I/O Chassis

1

1771 - ASB

1771 - DCM

1

Install Terminator Resistor
(cat. no. 1770XF)

12662

43