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HPOD
Customer Commands
Each target has a unique address, and each time the controller transmits, in a framed
'packet' of data, the address of the intended recipient target is included. All of the targets
receive the packet, but only one (the intended) will reply. The target enables its output
line driver, and transmits its return data packet back to the controller in the other direction
on the physically separate pair.
4.10 RS-485 (
Two differential pairs
Controller-to-target pair
Target-to-controller pair
4.11 RS-232
This is a much simpler configuration in which the controller device is connected directly
to the target via a two-wire-plus-ground connection. Controller-to-target data is carried,
via RS-232 electrical levels on one conductor, and target-to-controller data is carried in
the other direction on the other conductor.
4.12 B
P
ASIC
ROTOCOL
Whether in RS-232 or RS-485 mode, all data is transmitted as asynchronous serial
characters, suitable for transmission and reception by a UART. The asynchronous
character format is fixed at 8N1 (8 data bits, No parity, and 1 stop bit). Only two baud
rates are supported: 9600 baud and 19200 baud.
All data is transmitted in framed packets. The host controller is assumed to be a PC or
ASCII dumb terminal, which is in charge of the process of monitor and control. The
controller is the only device that is permitted to initiate, at will, the transmission of data.
Targets are only permitted to transmit when they have been specifically instructed to do
so by the controller.
All bytes within a packet are printable ASCII characters, less than ASCII code 127. In
this context, the Carriage Return and Line Feed characters are considered printable.
All messages from controller to target require a response (with one exception). This will
be either to return data that has been requested by the controller, or to acknowledge
reception of an instruction to change the configuration of the target. The exception to this
is when the controller broadcasts a message (such as Set time/date) using Address 0,
when the target is set to RS-485 mode.
)
FULL DUPLEX
SUMMARY
one pair for controller to target, one pair for target to controller.
has one line driver (controller), and all targets have line-receivers.
has one line receiver (controller), and all targets have tri-state
drivers.
:
4–4
Revision 1
MN/HPOD.IOM
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