Metasys Network Technical Manual 636
App. Notes: Network Communications Section
Application Note
Issue Date 1199
Dual N2 Bus
Introduction
Page
3
•
Overview
•
Terminology
*4
•
Hardware Requirements
*4
•
Software Requirements
4
3
Application Details
5
•
Overview
*5
•
Polling Times
•
Number of Devices
•
Independent Operation
5
Design Considerations
7
•
Calculating Number of Devices
7
•
Examples
5
*5
10
Installation Procedures
11
•
Connecting the Fast N2 Bus
*11
•
Defining Two N2 Buses on NCM
*12
References
*15
*Indicates those sections where changes have occurred since the last printing.
© 1999 Johnson Controls, Inc.
Code No. LIT-6363145
1
www.johnsoncontrols.com
2
App. Notes: Network Communications—Dual N2 Bus
Introduction
Overview
The Metasys Dual N2 Bus application provides the ability to define
two individual N2 Buses. The first N2 Bus is used for less critical devices
that require the standard level of alarm reporting (i.e., standard trunk). The
second N2 Bus is for critical devices that require very fast response times
(i.e., fast trunk). In fact, the system response time for the display of a
report at the Operator Workstation from the moment a change in the
object is sensed can be less than 2 seconds for certain critical alarm points.
Figure 1 shows an example of a Dual N2 Bus application.
NCU
(with NCM200)
Standard N2 Bus*
NEU
N2 Trunk=1
To more N2 devices
VAV
LCP
N2 Trunk=1 N2 Trunk=1
Fast N2 Bus*
NEU
N2 Trunk=2
LCP
N2 Trunk=2
NEU
N2 Trunk=2
VAV
DX-9100
N2 Trunk=2 N2 Trunk=2
* Standard N2 Bus connected to TB1 terminal block on communication terminal board of NCU.
Fast N2 Bus connected to TB2 terminal block on communication terminal board of NCU.
FASTN2
Figure 1: Example of the Dual N2 Bus
In this example, the standard bus connects a Network Expansion Unit
(NEU), a Lab and Central Plant (LCP) controller, Variable Air Volume
(VAV) controller, and other N2 devices not shown. The fast bus connects
two NEUs, LCP, DX-9100, and VAV. If the standard N2 Bus would go
offline for some reason, polling on the fast N2 Bus would continue
without any reduction in performance.
For technical details on the standard N2 Bus, refer to N2 Communications
Bus Technical Bulletin (LIT-636018) under the Network Communications
section of this manual.
App. Notes: Network Communications—Dual N2 Bus
3
Terminology
Unless otherwise specified, the information in this technical bulletin refers
to all NCM models in the NCM300 Series and the NCM200 with Network
Identity Module NU-NIM102-0 or higher.
Hardware
Requirements
The Dual N2 Bus application requires one of the following hardware
components:
•
NCM300 Series Control Module with:
-
•
MM-CVT101 RS-232 to RS-485 Converter
NCM200 with :
-
Network Identity Module (NU-NIM102-0 or higher)
-
N2 Submodule (NU-N2B101-0)
-
Power Supply (NU-PWR101-0)
Note: NCM200 parts listed are discontinued, and are available as repair
items only.
For technical details on the NCM300, refer to Network Control
Module 300 Series Technical Bulletin (LIT-6360251) in the Control
Modules section of this manual.
Software
Requirements
4
The only software requirement for the Dual N2 Bus application is Metasys
Person-Machine Interface (PMI) Release 6.0 or later. Any Metasys release
before 6.0 does not allow you to define the Port 2 Type as N2 under the
NCM Definition window.
App. Notes: Network Communications—Dual N2 Bus
Application Details
Overview
NCM200
Internally, the NCM200 contains the interface circuitry required for one
N2 Bus. The second N2 Bus is provided by installing a N2 Submodule
into the communications submodule slot of the NCM and connecting the
N2 Bus wires to TB2 on the communication terminal board. The N2 Bus
devices are then connected from the NCU in a daisy chain fashion. Next,
the N2 Bus devices are configured in software to be connected to the
second port.
Note: Since the N2 Submodule is a required component, the RS-232 and
MDM101 submodules cannot be used with the Dual N2 Bus
application. The NIM and backup battery use the other
two submodule slots.
NCM300
Use the RS-232 port and the MM-CVT101 converter for the second N2
port.
Polling Times
The standard N2 Bus and fast N2 Bus have independent polling cycle
timers, which provides the rapid change-of-state reporting. However, if
the NCM is busy performing control processes for the standard trunk, the
performance of the fast trunk may be decreased.
Number of
Devices
The second N2 Bus does not increase the number of devices, processes, or
objects that can be defined on one NCM. Therefore, you are only allowed
to put as many devices, processes, and objects on both trunks as if only
one N2 Bus is defined.
Independent
Operation
Both N2 Buses are generally independent. This means that a failure in the
operation of one trunk does not affect the operation of the other trunk.
Also, since the buses are separate, devices on the two different trunks may
have the same N2 address.
App. Notes: Network Communications—Dual N2 Bus
5
6
App. Notes: Network Communications—Dual N2 Bus
Design Considerations
Calculating
Number of
Devices
In general, you can connect five critical N2 Bus devices at poll Priority 0
to the fast N2 trunk. The system response for these devices will be
2 seconds or less. All other non-critical devices should be connected to the
standard N2 Bus. The system response for those devices will be greater
than 2 seconds; how much greater depends on N2 Bus traffic.
The fast N2 Bus, however, can probably accept more than five devices
and still have a 2-second response time. To figure out the system response
time for the fast N2 Bus, you need to consider:
• which priority levels the devices are assigned
• what mixture of devices, device types, objects, and commands are
being used
Priority Levels
Device polling on the N2 Bus is governed by polling priorities. There are
four priority levels, chosen when the device is defined: 0, 1, 2, and 3,
with 0 as the highest. For example, a device assigned at Priority 0 is polled
more often by the NCM than a device at Priority 1. Table 1 below
illustrates the minimum polling cycles for an N2 device based on its poll
priority. For example, the NCM polls a DCM assigned to Priority 1 no
faster than once every 0.5 seconds, even if the NCM has enough time and
capacity to poll it faster. A device at poll Priority 3 is polled no faster than
once every 4 seconds, and so forth.
Table 1: Minimum Polling Cycles in Seconds
Poll Priority Assigned to N2 Device
Minimum Polling Cycle for Online*
N2 Device (seconds)
0
0.33
1
0.5
2
1.0
3
4.0
*
Polling may be interrupted for up to 0.5 seconds while waiting for a response from
an offline device.
Note: Table 1 shows minimum polling times for online devices only. An
offline device will cause a polling interruption of up to 0.5 seconds
while the NCM waits to determine that the device is offline.
Therefore, each offline device will severely extend the minimum
polling cycles for the online devices.
App. Notes: Network Communications—Dual N2 Bus
7
Mixtures
Polling also depends on the number and type of devices, objects, and
commands on the N2 Bus. Table 2 lists the type of N2 communication and
how often each item is polled. For example, it takes the NCM
0.05 seconds to poll a Digital Control Module (DCM). A DR-9100,
however, takes 0.1 second to poll.
Table 2: Polling Table
Type of N2
Communication
Time to Complete Poll
(seconds)
How Often Polled
Online Poll of DCM,
XM, N2OPEN,
DX-9100, or
DC-9100/LCP
0.05
once in a polling
cycle
Online Poll of
DR9100, XT-9100, or
XTM101
0.1
once in a polling
cycle
Poll of AD* or BD*
Object that is
Associated with
CSG Attribute
0.05
every 30 seconds or
every 4 seconds for
binary attributes
Poll of any Attribute
used to Trigger
Process
0.05
every 30 seconds or
every 4 seconds for
binary attributes
Poll of AI* with
Warning Limits
0.05
every 30 seconds
Poll of AI* Mapped to
System 91 Device
0.05
after COS occurred
Poll of any Input
Point Displayed on
OWS
0.05
every 20 seconds
Poll of any Point in a
CS Object Displayed
on OWS
0.05
every 20 seconds
0.05
every 60 seconds
Poll of ACM Object
Command from
Process, Time
Schedule, or
Operator
0.05 (N2OPEN, DCM, XM)
0.1 (XT-9100, XTM)
0.2 (DR-9100, DX-9100, or
DC-9100/LCP)
dependent on
process, time
schedule, or
operator
*AD = Analog Data
BD = Binary Data
AI = Analog Input
To calculate the system response time for a fast N2 Bus:
1. Write down how many and the types of devices, objects, and
commands you want to define on the fast N2 Bus. Example:
• two DCMs
• ten XT-9100s
• five attributes that trigger processes
• five BDs associated with CSG attribute
• five AIs mapped to System 91 device
8
App. Notes: Network Communications—Dual N2 Bus
2.
Using the figures in Table 2, calculate the polling cycles for each
device by:
Number of Devices x Time to Complete Poll = Poll Cycle
Example:
two DCMs:
ten XT-9100s:
3.
2 x 0.05 = 0.1
10 x 0.1 = 1.0
Using the figures in Table 2, calculate the polling cycles for each
object or command by:
Number of Objects/Commands x Time to Complete Poll = Poll Cycle
Worst case example:
five attributes that trigger processes: 5 x 0.05 = 0.25
five BDs associated with CSG attribute: 5 x 0.05 = 0.25
five AIs mapped to System 91 device: 5 x 0.05 = 0.25 (after COS)
4.
Total the poll cycles for all the devices, objects, and commands. This
total is the system response time of the fast N2 Bus. Example:
0.1 + 1.0 + 0.25 + 0.25 + 0.25 = 1.85 seconds
(worst case total system response time)
If you are trying to achieve a system response time of less than 2 seconds,
be sure the complete polling cycle is no longer than 1.5 seconds. The
remaining 0.5 second is needed for time synchronization messages and
offline processing (i.e., N2 processing overhead).
App. Notes: Network Communications—Dual N2 Bus
9
Examples
The following are three examples of correctly configured N2 Bus
installations, which will provide various N2 Bus response times. They are
“worst case” scenarios in which system response will be no slower than
the totals calculated. The examples use the information given in Table 2.
Example One
Given:
two DCMs:
four XMs:
ten AIs with warning limits:
four time schedule commands on DCM:
Total:
Example Two
Given:
six DX-9100s:
six XT-9100s:
20 ADs associated with CSG:
Total:
Example Three
6 x 0.05 second = 0.3 second
6 x 0.1 second = 0.6 second
20 x 0.05 second = 1 second
1.9 seconds (worst case)
Given:
one XM:
one LCP:
two DR-9100s:
20 input points that display on OWS:
six LCP process commands:
Total:
10
2 x 0.05 second = 0.1 second
4 x 0.05 second = 0.2 second
10 x 0.05 second = 0.5 second
4 x 0.05 second = 0.2 second
1 second (worst case)
App. Notes: Network Communications—Dual N2 Bus
1 x 0.05 second = 0.05 second
1 x 0.05 second = 0.05 second
2 x 0.1 second = 0.2 second
20 x 0.05 second = 1 second
6 x 0.2 second = 1.2 second
2.5 seconds (worst case)
Installation Procedures
Connecting the
Fast N2 Bus
The following is an overview of the steps to install the fast N2 Bus. For
further details on the N2 Bus, refer to the N2 Communications Bus
Technical Bulletin (LIT-636018) under the Network Communications
section of this manual. For more information on the NCM, refer to
Network Control Module 300 Series Technical Bulletin (LIT-6360251) in
the Control Modules section of this manual.
NCM200
These steps presume you want to install the fast N2 Bus to the second N2
Bus terminal block (TB2) on the communication terminal board of the
NCU. However, you may use the first N2 terminal block (TB1) instead there is no restriction in which terminal block you use. If you connect the
fast N2 Bus to TB1, be careful to make your connections and definitions
for using TB1, not TB2.
1.
Install the N2 Submodule into the communications submodule slot
(Port 2) on the NCM.
If this NCM is at the end of the fast N2 Bus, set the End-of-Line
(EOL) switch on the N2 Submodule to In. If this NCM is not at the
end of the fast N2 Bus, set the EOL switch to Out.
Set the Channel A/B switch to B, since the fast N2 Bus will be
connected to TB2 on the communication terminal board.
Note: For the NCM200, you cannot select Channel A on the N2
Submodule, because the N2 Bus circuitry for Channel A is
internal on this NCM model.
2.
Connect the fast N2 wires to TB2 (Figure 2).
Make all other necessary N2 Bus connections to the devices for both
trunks.
NCM300
Follow these steps to install the fast N2 Bus on the NCM300:
1.
Connect the RS-232 straight-through cable from NCM300 Port 2 to
an MM-CVT101 Converter.
2.
Connect the fast N2 Bus to the MM-CVT101.
App. Notes: Network Communications—Dual N2 Bus
11
TB2
(For Fast N2 Bus*)
HRD 6
GRD
SFT
GRD
4
5
Out
TB2
GRD
SFT
GRD
N2(-)
4
1
N2(+)
3 SFT
GND
2
N2BREF
In
HRD 6
3 SFT
GND
N1
TB1
(For Standard N2 Bus)
5
2
N2(-)
1
N2AREF
N2(+)
TB1
Standard TBC
TB2
TB1
NCM-Only TBC
* Alternatively, the fast N2 Bus can use TB1.
N2TBC
Figure 2: TB1 and TB2 Connections on TBC
Defining
Two N2 Buses
on NCM
The method for defining two N2 Buses on an NCM depends on whether
this NCM is defined or undefined. If the NCM is already defined and you
want to add a second N2 trunk, use Data Definition Language (DDL). If
you are defining a new NCM, use DDL or the Metasys PMI to define the
two N2 trunks.
After editing the global DDL file to define a second N2 Bus on an existing
NCM, you must compile the Global DDL file, download the Global
database, then redownload the NCM database. If you do not redownload
the NCM, the second N2 Bus will not come online.
Using DDL
When defining the NCM offline with DDL, specify “N2” in the global
DDL file for the Port 1 Type and the Port 2 Type. Example:
NC "NCM-1","NCM-1 4th Floor",0,0,1,1,"N2","N2"
This line defines an NCM called NCM-1, which will use two separate N2
trunks.
Also, for each N2 device that will be connected to the fast N2 Bus, specify
“2” on the Address line as the trunk you are using for the fast trunk. Also,
specify “0” as the polling priority (the highest). Example:
XM "NCM-1","XRL4","Left XRL"
ADDRESS 4,2,3,0
This line defines XRL4, which is connected to the second (fast) N2 trunk
of NCM-1. It will be polled using Priority 0.
12
App. Notes: Network Communications—Dual N2 Bus
Using Metasys
PMI
When defining the NCM online with the Operator Workstation, enter
“N2” in both the Port 1 Type and Port 2 Type fields under the NCM
Definition window. Example:
NCM Definition
Item
Edit
View
Action
Go To
Help
Accessory
HDQTRS
DEVICES
DEVICES
Object Name
Expanded ID
NC Language
NCM-1
NCM-1 IN MECH ROOM
ENG
Graphic Symbol #
0
Operating Instr. #
0
Hardware
NC Subnet Address
NC Node Address
Port 1 Type
Port 2 Type
NT Baud Rate
1
3
N2
N2
9600
Port 1 Baud Rate
Port 2 Baud Rate
NCMDEF
Figure 3: Defining Second N2 Bus in NCM Definition Window
Also, for each N2 device that will be connected to the fast N2 Bus, enter
the NC trunk number as “2.” Also, specify “0” as the polling priority (the
highest). Example:
Expansion Module Definition
Item
Edit
View
Action
Go To
Help
Accessory
HDQTRS
NCM-1
PANEL_67
PANEL_67
MECH
XRM-1
XRM-1 IN MECH ROOM
NCM-1
System Name
Object Name
Expanded ID
NC Name
Graphic Symbol #
0
Operating Instr. #
0
Hardware: N2
NC Trunk Number
Device Address
Poll Priority
Device Type
2
4
0
XRM
Comm. Disabled
N
Flags
Auto Dialout
N
XRMDEF
Figure 4: Assigning XRM to Second N2 Bus
App. Notes: Network Communications—Dual N2 Bus
13
14
App. Notes: Network Communications—Dual N2 Bus
References
This document provides an overview of defining a second N2 Bus.
General information on the N2 Bus, NCM, and NCU can be found in other
documents. Table 3 is a list of references that you may find helpful if you
have questions on any components of the N2 Bus.
Table 3: Other Helpful References
Topic
Metasys Network
Technical Manual
(FAN 636) Section
Document Name
General N2 Bus
Information
Network Communications
N2 Communications Bus
Technical Bulletin
(LIT-636018)
NCM200
Information
Control Modules
Network Control Module 200
Series Technical Bulletin
(LIT-636025)
NCM300
Information
Control Modules
Network Control Module 300
Series Technical Bulletin (LIT6360251)
NCU Information
Network Units
Network Control Unit/Network
Expansion Unit Technical
Bulletin (LIT-636020)
App. Notes: Network Communications—Dual N2 Bus
15
Notes
Controls Group
507 E. Michigan Street
P.O. Box 423
Milwaukee, WI 53201
16
App. Notes: Network Communications—Dual N2 Bus
www.johnsoncontrols.com
FAN 636
Metasys Network Technical Manual
Revision 10.0
Printed in U.S.A.