MSK Modem
7
MX809
4 General Description
The MX809 is an intelligent, half-duplex 1200-baud MSK Modem, which operates under C-BUS control. This
modem provides software selectable checksum generation and error checking in accordance with MPT1327.
In TX Mode the MX809 will:
1. a) Accept from the host and transmit 8-bit bytes of data as instructed (preamble, sync, address, and data), or
b) Internally calculate and inset a 2 byte checksum based on the preceding 6 bytes of data, or
c) Disable the internal checksum generator and continuously transmit the data supplied.
2.
Transmit 1 hang-bit and go to TX idle when all loaded data bytes have been transmitted.
In RX Mode the MX809 will:
1.
Detect and carry out bit synchronization within 16 bits.
2. a) Search and detect the user-programmed Sync (or its opposite logic sense) Word and carry out frame
synchronization. Data will then be output in 8-bit bytes via the RX Data Buffer.
b) Use the received checksum to calculate the presence of any errors, setting the Status Register accordingly.
3.
Make the incoming data directly available via the RX Data Buffer (RX Freeformat), overriding the synchronization
requirements.
RX input timing is achieved by recovering an RX clock from the incoming data stream. Output tones are
timed to the internally generated TX clock. Filter, register clocks, and transmit MSK tone frequencies are
derived internally from the external Xtal or clock pulse input.
A 4.032MHz Xtal or clock input is required for compliance with the MPT1327 Signaling Specification. Note:
All information contained in this data bulletin is specified using a 4.032MHz Xtal, 1200bps baud rate, with
Mark and Space frequencies of 1200Hz and 1800Hz. The MX809 has a non-committed amplifier on-chip for
general applications in the DBS 800 series.
5 Controlling Protocol
Control of the functions within the MX809 MSK Modem is by a group of Address/Commands and appended
data instructions from the system microcontroller. Two separate MSK Modems can be addressed. The use
of these A/Cs is detailed in the following paragraphs and tables.
Command Assignment
Address/Command
Binary
Command Data
HEX
01
MSB
LSB
General Reset
00000001
01000000
01000001
01000010
01000011
01000100
Control Register bits set to logic “0”
1 byte instruction to Control Register
1 byte reply from Status Register
1 byte of data from RX Data Buffer
1 byte of data to TX Data Buffer
Write to Control Register
Read Status Register
Read RX Data Buffer
Write to TX Data Buffer
Write to SYNC Program
40
+
+
+
+
+
41
42
43
44
2 bytes of SYNC Word to SYNC
Program. Register
Table 5: Modem No. 1 C-BUS Address/Commands – (Address Select input at a logic “0”)
5.1 Address/Commands
Instructions and data transactions to and from the MX809 consist of an Address/Command (A/C) byte
followed by either further instructions or data, or a Status or RX Data Reply.
Control and configuration is by writing instructions from the microcontroller to the Control Register [40 (48 )].
H
H
Reporting of the MX809 configuration is by reading the Status Register [41 (49 )]. Instructions and data are
H
H
transferred via C-BUS in accordance with the timing information given in Figure 11.
Data to be transmitted as MSK is sent to the TX Data Buffer via the Command Data line. Received data is
read from the RX Data buffer via the Reply Data line.
Instructions and data transactions to and from this device are preceded by the relevant A/C.
ꢀ1998 MX-COM, Inc.
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480036.004
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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CMLMICRO [ CML MICROCIRCUITS ]
