Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 66)

Choosing Communication
Chapter 5
5-8
Initial testing was done with one PLC-5 processor writing data to another
PLC-5 processor. The response time was recorded. Additional PLC-5
processors were added to the network, each writing the same amount of
data to a PLC-5 processor at the next highest station address. Four
separate tests were run using data transmissions of 50, 100, 250, and
500 words.
Application Guidelines
Consider the following application guidelines when configuring a DH+
link for your system.
Configure the number of nodes on your network dependent on the size
and frequency of messages exchanged between devices.
Limit the number of nodes on your network when you are trying to
achieve fastest control response time.
Do not add or remove nodes from the network during machine or
process operation. If the network token resides with a device that is
removed, the token may be lost to the rest of the network. The network
is automatically re-established, but it could take several seconds.
Control would be unreliable or interrupted during this time.
Include watchdog timers in logic programs for DH+ transfer of data (to
provide an orderly shutdown if failure occurs).
Do not program processors online during machine or process operation.
This could result in long bursts of DH+ activity that could increase
response time.
When possible, add a separate DH+ link for programming processors to
keep effects of the programming terminal from the process DH+ link.
Connecting Devices to DH+ Link
You can connect devices on a DH+ link with:
daisy-chain connection
trunkline/dropline connection
See Figure 5.7. Also, see the Data Highway and Data Highway Plus Cable
Guide, publication 1770-6.2.1, for complete network wiring instructions.