If you allocate a static IP address to your computer and if the static IP address you allocate is somewhere in the DHCP range then you WILL HAVE PROBLEMS.

1. The SMC modem blocks access to the internet for that computer. We have experienced this issue on multiple occasions.
2. The SMC modem might allocate the same IP address to a new DHCP client so that you end up with duplicate IP addresses. We have seen this occur more than once.

Another issue on the Modem is the following: You cannot make the DHCP range smaller if the modem has already allocated an address outside the new range. eg. old range = .100 to .150     there is already .148 on the network and now you try and change the range to .100 to .120. No go. It will not work. Disable the network connection and Disconnect all computers. Reboot the modem. Change the range. Repower and reboot all.

“The Present_Value property shall always have a value greater than zero.”

Gateways often boot with all data set to zero and may report this invalid state until the data has been updated using the Non-Bacnet data.

When the product is shipped the internal jumper is set to LinkNet. Despite this BACnet MSTP is active and if you connect a MSTP client you can read and write the BACnet objects. What you cant do until you change the jumper is discover the device. It appears the only effect of the jumper is to enable the reply to a who-is.

Did you know that with the CAS BACnet Explorer you can add a device manually and then discover its objects and properties. Using this feature the DFM-200 was ‘discovered’ even with the protocol selection jumper in the wrong position.

What happens if you want to serve some/all of the bits that form a 16 bit register. ie. Your client reads a 16bit register but you want to serve those bits as separate binary objects.

Here is an example

• A series of 16 bit numbers
• A series of bits

It depends on what kind of operation access the Data Array. If it’s a 16 bit or analog number type operation then it addesses 16 bit numbers. If the operation is a bit operation like for a binary data point then the operation addresses each bit.

Therefore DA_PACKED[0] is ambiguous.

If you connected a server Map Descriptor to that point and the type is an Analog In/output then it means the 16bit number found at DA_PACKED[0].

If you connected a server Map Descriptor to that point and the type is an Binary In/output then it means the bit number found at DA_PACKED[0] and DA_PACKED[15] is the 16^th bit. DA_PACKED[16] is the 1^st bit of the next 16 bit number…

If that seems to complicated then add one more move:

Data_Arrays

This move moves the 16 bits for DA_PACKED[0] to 16 separate bits with unambiguous offsets and you can use those in the server map descriptors.

Heads Up

Preloads

Moves

The following applies for both half and full duplex RS485.

You can have any number of protocols on the same 485 trunk provided that two or more devices do not talk at the same time.
The consequences of this statement are
1. You can only use more than one protocol if they are poll/response type protocols like Modbus Rtu or Rockwell DF1.
2. If you have a token passing protocol (such as Bacnet mstp) you cannot use another protocol on the same trunk
3. Only one device can be the master for the multiple protocols. The reason is that the master decides when to poll and how long to wait for a response.

Thus, If you have full control over one rs485 port you could use that port to send a poll using protocol#1, wait for a response and then send a poll using protocol#2. If you do not have full control (ie. You are letting two applications which are not co-ordinated share the port) then you cannot run two protocols.

2.i16-1.i32

2.i16-1.i32-s

2.i16-1.i32-sw

2.i16-1.i32-sb

Each of these functions takes 2x 16 bits numbers to form a 32 bit number. Each processes the bytes in a different order.

Practical Tip: The easiest way to determine which function to use is to experiment. Look at the values in the FieldServer Data Arrays. If the values are obviously wrong try the other move functions. (Don’t forget that some numbers may be scaled so the number you see in the Data Array may 10x or 100x too big / small).

Example:

In the move below if

DA_B01_REG[21] == 1 and

DA_B01_REG[22] == 2

Then

DA_B01_INT32[21] == 131073

Explanation

1 + 65536* 2 = 131073

Or In Hexadecimal

0×0001 + 0×0002 * 0×10000 = 0×20001

Moves

Source_Data_Array ,Source_Offset ,Target_Data_Array ,Target_Offset ,Length ,Function

DA_B01_REG ,21 ,DA_B01_INT32 ,21 ,2 ,2.i16-1.i32

By the way, the length is 2 because the move must process two values from the source.

Example:

DA_B01_REG[21] == 1 and

DA_B01_REG[22] == 2

• Transfer size – More then x BYTES are collected or
• Latency timer – More then n Milliseconds (ms) expirer.

By default most ‘off the self’ USB to serial converters have a latency timer of 50ms and a transfer size of 4096 BYTES

The can be a major problem for PC utilities monitoring a serial network. The PC doesn’t get the BYTES fast enough to respond to the serial device before it times out.

For example:

On a network with a BACnet MSTP thermostat and a RS485 to USB converter connected to a PC. The BACnet MSTP thermostat will send a poll to the PC and will expect the PC to respond within 100ms. If the thermostat does not receive a response within this time the thermostat will assume that the device has gone offline. When the USB to 458 converter receives the message it will stay in its buffers for 50ms before being sent to the PC. Depending on the message it may take longer then 50 ms for the PC to respond to the poll and the thermostat will consider the PC offline.

Luckily we can set the Transfer size, and latency timer.

Most USB to 485 devices that I have used have the ability to set the transfer size and the latency timer.

1. Start menu–> Settings –> Control panel –> device manager –> Ports (COM & LPT) –>{Select your USB to RS485 converter}
2. Right click and select “Properties”
3. Select the “Port Settings” tab
4. Click the “Advanced” button 
5. Change the Latency Timer (mSec) to 1 or the lowest possible setting.
6. Change the USB Transfer sizes to 64 or the lowest possible settings
7. Save and close.

The question is: How do you match requirements of a project to the capabilities of the devices being installed ? The Answer – in BACnet – is BIBBS.

A BIBB is a Bacnet Interoperability Building Block.

Continuing with our example: Say your controller needs to read the set point on a thermostat to perform its control. Then the controller needs to support a BIBB called DS-RP-A. This isn’t enough. The thermostat must be able to respond so it needs to support a BIBB called DS-RP-B. DS stands for Data Sharing. RP stands for Read Property. The A and the B stand for Client (A) and Server (B).

The outdoor temperature on a HVAC controller could come from two places. A local sensor connected to the unit or a remote value sent via BACnet. In this case you would want to match the BAS controller and HVAC controller with BIBBS DS-WP-A and DS-WP-B (DataSharing-WriteProperty-A or B for Client and Server).

Thus, if you buy a great controller that supports Conditional and Range Reads you would want to buy field devices that support these services. DS-RPC-A/B for DataSharing-ReadPropertyConditional-Client/Server.

Abbreviation BIBB Category
DS        Data Sharing
AE        Alarm and Event Management
DM       Device Management
DM and NM are part of the same category.
NM       Network Management
T          Trend
SCHED Schedule

TIP : Device A and Device B. All the BIBBs end in ‘-A’ or ‘-B’. BACnet refers to the A device and the B device. The A device in this context is a device acting as a client. The B device means a device acting as a server. In BACnet devices can be both clients and servers since almost all devices can read data from each other.

A complete table of BIIB’s is available at: http://www.chipkin.com/articles/bacnet-bibbs-table-bacnet-interoperability-building-blocks