Beijer Electronics SCOM RBC EN - Manual (Page 10)

Protocol Description and Timings
10 Beijer Electronics, MAEN993
Conditions for Response Message
The conditions for a response message generated by the Beijer Electronics RBC are
described below:
Delayed Response
If a Beijer Electronics RBC receives an SCOM message with a broadcast address from
the RS485 interface and the command is completed, the generated response message
is sent after a delay time. This is required, because many devices can be attached to
the RS485 bus, but only one device can claim the line for its communication. The
delay guarantees that each response message is sent one after one, even if all devices
have received the broadcast message and processed it at the same time, avoiding a col-
lision on the RS485 bus.
The length of the delay time depends on the device address and maximum length of
a response message, and is calculated according to the following formula:
Interface Address condition Command status Response
RS232 Address does not match
device address not EXECUTED No response
not EXECUTED No response
Address matches device
address if COMPLETED ACK
if FAILED NAK
Address is Broadcast
address (0xFF) if COMPLETED ACK
if FAILED NAK
RS485 Address does not match
device address not EXECUTED No response
not EXECUTED No response
Address matches device
address if COMPLETED ACK
if FAILED NAK
Address is Broadcast
address (0xFF) if COMPLETED Delayed ACK
if FAILED No response
USB Address does not match
device address not EXECUTED No response
not EXECUTED No response
Address matches device
address if COMPLETED ACK
if FAILED NAK
Address is Broadcast
address (0xFF) if COMPLETED ACK
if FAILED NAK
(2.5 + Lr) x 10 x N
Te =
b
Te: Broadcast command response [s]
Lr: Maximum length of response message
N: Device address + 1
b: Baud rate [bits/second]