Service manual

EXTERNAL SERIAL CONTROL PROTOCOL
B-4
April 2001
Part No. 001-9800-203
Formatted data string:
0xba, 0x01, 0x02, 0x37, 0x10, 0x02, 0x33, 0xFF,
0x10, 0x00,0x10, 0x00, 0x10, 0x02, 0x7e
NOTE: The checksum is 0x10 and it is also followed
by an ESC character.
B.2.3 FRAME ADDRESSING
All devices attached to the bus must be address-
able via a broadcast address and a unique address. The
addresses are allocated as follows:
The broadcast address is used by the Subscriber
Unit at power-up to determine what devices are
currently residing on the bus and to assign their
respective addresses. The Subscriber Unit must select
the lowest valid device address field (0x01) when it
powers up.
B.2.4 FRAME TYPES
The three frame types used in this protocol are as
follows:
Command Frames
Command frames are used to directly command
or request the destination to perform a specific
function
or operation. Commands include items such
as setting protocol options, powering on or off, and
changing operating modes.
Command frames are always responded to by an
ACK or NAK message from the receiver and they
cannot contain a broadcast destination address.
Event Frames
Event frames are used to indicate that certain
events or conditions have occurred. The subscriber
unit is the arbitrator of events. An event sent to the
subscriber unit is a notification that the external device
has had that event occur and the subscriber unit should
take appropriate action. Events broadcast from the
subscriber unit are notifications that the event has
occurred and been arbitrated.
Event frames with a non-broadcast source and
destination address are always responded to by an
ACK or NAK message from the receiver. Broadcast
event frames are never responded to by an ACK or
NAK message.
Information Frames
Information frames contain non-event related
data. These frames are generally sent by the subscriber
unit and usually in response to an external device
command frame.
Information frames are never responded to by an
ACK or NAK message. If the message contains
general radio state information, it has a broadcast
destination address. If the message contains informa-
tion relating to one or more parameters included in the
command requesting the information, it has a specific
destination address.
Note that with a command that is both responded
to by an ACK message and causes an information
frame to be generated, message ordering is arbitrary
(the information frame may be sent before or after the
ACK message).
B.2.5 FRAME ACKNOWLEDGMENT
Only frames indicated can be acknowledged via
the acknowledgment opcode. The acknowledgment
must be received by the destination device within 500
milliseconds of reception. If the source device does
not receive any response within the defined time, the
source must retransmit the last message.
Address Addressee
0x00 Reserved
0x01 Subscriber Unit
0x02 External Device 1
0x03 External Device 2
0x04 External Device 3
0x05 External Device 4
... External Device ...
0x07 External Device 6
0x08-0xA9 Reserved
0xAA Broadcast Address
0xAB-0xFF Reserved