1200/2400bps MSK Modem for Trunked Radio Systems
6
MX429A
4 General Description
4.1 Modems in Mobile Data Signaling
4.1.1 Digital Code Format
The MPT 1327 Signaling Standard for Trunked LMR Systems protocol is used by the MX429 for
communication between a Trunking System Controller (TSC) and users' radio units. These data stream
formats are summarized in Figure 3.
Preamble
SYNC or SYNT
For bit sync.
101010...10..- bit reversals
Minimum 16 bits, ending in
logic'0'
SYNC Word
1100010011010111
SYNT Word
Address Code
Word
Optional Data
Code Words
0011101100101000
64 Bits
Address Code Word Structure
to
(Bit number 1 is transmitted first)
49 to 64
Bit No.
1
2
8
9
to 48
40
No. of Bits
1
7
16
Address
&
Check Bits
(Checksum)
Bit Name
Logic '1'
User Identity
Data
Figure 3: Tx and Rx Data Stream
4.1.2 Operation
The MX429A can be used for Full-Duplex operation with the host microprocessor only having to operate on
the data while the modem (MX429A) handles all other signaling routines and requirements.
In the Tx mode the MX429A will :
1. Internally generate and transmit a preamble – bit reversals, for system bit synchronization.
2. Accept from the host, and transmit, a 16-bit 'SYNC' or 'SYNT' word.
3. Accept from the host, and transmit, 6 bytes of data (Address Code Word):
A. Upon a software command, internally calculate and transmit a 2-byte checksum based on the
previous 6 data bytes.
B. Upon a software command, disable internal checksum generation and allow continuous data
transmission.
4. Transmit 1 'hang bit' and go idle when all loaded data traffic has been sent (followed by a "Tx Idle"
interrupt).
In the Rx mode the MX429A will:
1. Detect and achieve bit synchronization within 16 bits.
2. Search for and detect the 16-bit 'SYNC'/'SYNT' word.
3. Output all received data after 'SYNC/SYNT,' in byte form.
4. Upon a software command (Rx Message Format), use the received checksum to calculate the
presence (if any) of errors, and advise the host with an interrupt and a 16-bit Syndrome word.
Note: In Rx, a software command is used to determine whether a 'SYNC'/'SYNT' word is required after
every 8 (6 data + 2 checksum ) received bytes, or "data" is received continually.
Normally the 'SYNC' word is used on the Control data channel and the 'SYNT' word is used on the
Traffic data channel.
© 1998 MX-COM Inc.
www.mxcom.com Tel: 800 638-5577 336 744-5050 Fax: 336 744-5054
Doc. # 20480128.007
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
All trademarks and service marks are held by their respective companies.
CMLMICRO [ CML MICROCIRCUITS ]
