Maple Systems STEPware-100 - Manual (Page 41)

When using Network mode, always follow these rules:
1. Every OIT on the network must be assigned a unique network address.
2. Every OIT on the network must be programmed to use the same line terminator.
3. Always have the host controller send a line terminator immediately before sending an
OIT network address. There are two reasons for this:
• If one of the OITs on the network suddenly loses power and reinitializes, it will not know what
“state” the communications session is in. Therefore, it will not respond to the host controller
until the host controller sends a line terminator.
• If any other characters are present on the data line between the time that the host controller
sends the line terminator and the network address, the OIT that the host controller is attempt-
ing to communicate to may not “log on” because the OIT thinks that the host controller is
logged on to another OIT.
Receiving Data from the OITs
When the host controller sends data that requires a response from the OIT, the OIT
immediately responds (unless turnaround delay is used). The OIT responds by sending its
hexadecimal network address as two ASCII characters followed by the requested data and
the line terminator. Each command that requests data is answered separately by the OIT.
As in Block mode, any OIT keypad input is sent to the OIT’s display and the Keyboard Input
Buffer. However, once the OIT’s ENTER key is pressed, the contents of the Keyboard Input
Buffer are transferred to the Keyboard Output Buffer and the OIT no longer accepts keypad
input until the host controller either polls or clears the OIT’s Keyboard Output Buffer. If an
attempt is made to enter additional data, the OIT sounds an error beep. If a function key is
pressed that has the Send Message Immediately setting enabled, then the output is sent
directly to the Keyboard Output Buffer along with any other contents of the Keyboard Input
Buffer, just as though the operator had pressed the ENTER key. The OIT will no longer
accept keypad input until the host controller either polls or clears the OIT’s Keyboard Output
Buffer. If an attempt is made to enter additional data, the OIT sounds an error beep.
Refer to Appendix A: Control Commands for information on the Clear Output Buffer and
Poll OIT Buffer control commands.
Sending the Same Data to all OITs
The host controller can send an identical message to all of the OITs on the network by
using the global broadcast address of “00”. The OITs do not transmit any data to the host
controller when the global address is used; this prevents the OITs from corrupting each
other’s messages by trying to talk at the same time. After sending a global broadcast,
before the host controller can begin a session with one particular OIT, the host controller
must send the line terminator to “log off” all of the OITs on the network.
Network Addressing
The addressing range allowed for networked OITs is from 1 to 255. This implies that up to
255 OITs can be connected to one network. However, the actual number will likely be less,
and is due to the loading characteristics of the network connection. Factors such as baud
rate, impedance and capacitive loading of the communications line, line impedance of the
RS-485 drivers, and total number of OITs on the network all affect performance. If network
performance becomes degraded, you may need network boosters or repeaters to increase
the number of OITs on the network. For more information on sources for network boosters
or repeaters, contact Maple Systems Technical Support at 425-486-4477.
38 STEP1 Protocol Operation Manual
1010-0096, Rev. 04