Service manual

DATA INTERFACE DESCRIPTION
A-8
April 2001
Part No. 001-9800-203
A.4 DATA MODEM OPERATION
A.4.1 DATA GROUP SUPPORT
The 9800-series radio includes support for data
groups. A group programmed as a data group has the
following properties:
Muting
Whenever the radio is on a group flagged as a
data group, both the speaker audio and microphone
audio are muted. This prevents the user from hearing
or interfering with data transmissions.
Data Group Hunt
When the radio detects a DATA PTT or DATA
PTT REVERT, it “hunts” for a data group to transmit
on. The hunt procedure is as follows:
1. If the current revert (currently or last selected) group
is a data group, transmission occurs on that group.
2. If the current revert group is not a data group, the
revert system is checked for a data group starting
with the first assigned group. If one is found, trans-
mission occurs on that group.
3. If the current revert system has no data groups, the
current bank is checked for a data system and group.
If a data system and group are programmed, trans-
mission occurs on that group.
4. If all of the above fail, the error tone sounds and “U”
(low tier models) or “NO DT GP” (mid and high tier
models) is displayed.
Voice Group Revert
If the radio is on a data group when a normal
microphone PTT is detected, it attempts to revert to a
voice group using the following procedure:
1. If the revert (currently or last selected) system and
group are a voice group, transmission occurs on that
group.
2. If the revert system and group are a data group,
transmission occurs on the last user selected system
and group.
3. If the last user selected system and group are a data
group, the radio sounds the error tone and displays
“U” (low tier) or “DATA GRP” (mid/high tier).
A.4.2 DATA ARQ MODE
Introduction
Data ARQ, as used in a trunked radio system, is a
method of rapidly changing between the transmit and
receive modes without handshaking. This allows data
devices that send short messages and expect imme-
diate acknowledgments to get these acknowledgments
without experiencing normal trunking delays.
Modem Initiated Transmission:
1. The modem initiates a “Data” transmission by
asserting the DATA PTT line followed by asserting
the DATA ARQ line. The DATA PTT line must
remain asserted for the entire data transmission and
acknowledge session.
2. After a successful access of the channel/system, the
modem must release the DATA ARQ line as it trans-
mits the data.
3. The modem must assert the DATA ARQ line for
reception of any ACKs or NACKs. During this time
the radio does not decode any subaudible data.
4. For all subsequent assert to release transitions on the
DATA ARQ line, the radio transmits with
subaudible data.
5. For all subsequent release to assert transitions on the
DATA ARQ line, the radio receives without
decoding subaudible data.
6. The data session is completed by the release of the
DATA PTT line. At this time the mobile transmits
the turnoff code and returns to the idle state.
Modem Initiated Reception:
1. The modem initiates a “Data” reception by asserting
the DATA ARQ line during the reception of a “call”
on a “Data Group”. The DATA ARQ line must
remain asserted for the entire data transmission and
acknowledge session.