CMX969D5 MX-COM, Inc., CMX969D5 Datasheet - Page 28

• Manufacturer Part Number: CMX969D5
• Description: MOTIENT/ARDIS RD-LAP MDC4800 Modem
• Manufacturer: MX-COM, Inc.

MOTIENT
5.2 Rx Control Procedure
The following procedure illustrates how the CMX969 can be controlled to receive one or more messages in
MDC mode. RD-LAP mode is similar except that the first block of each message will be a Station ID block.
Note: Once a Frame Sync pattern has been detected with AFSD then if the radio is receiving concatenated
messages and if the system does not employ Single Frequency Reuse techniques subsequent Frame Sync
patterns may be detected by using a SFS task (04h) instead of AFSD. Using SFS will reduce the very small
chance of a false Frame Sync detection. Not that the SFS task signals that it has found a Frame Sync pattern
by setting the Status Register BFREE bit to 1, whereas AFSD sets the AFSDET bit.
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4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
Step
0
1
2
3
4
5
Switch radio onto receive channel.
CMX969 Mode Register
SSIEN bits should be set as required, other bits 0.
Control Register should have CKDIV bits set as
required, MDC bit = 1, all other bits 0.
Write RESET + AFSD (87h) to Command
Register
Wait for Status Register AFSDET bit to go to 1
Write RHB + AFSD (82h) to Command Register
Wait for Status Register AFSDET or BFREE bits
to go to 1
If AFSDET bit =1 then a new Frame Sync has
been detected so go to step 3.
If AFSDET = 0 and BFREE = 1, the previous Rx
task (RHB and RILB) has completed. Read Rx
data from Data Buffer. Check the Status Register
CRCERR bit if it was a Header block or the ‘last’
Data block.
To receive and decode the next block from this
Rx message write AFSD + RHB or RILB (82h or
83h) to the Command Register and go to step 4
If we have received all of the blocks in the
message or wish to ignore any following blocks in
this message then write AFSD (80h) to the
Command Register and go to step 2.
SM
/ARDIS
SM
RD-LAP
www.mxcom.com Tel: [phone] 744 5050 Fax: [phone]
TM
MDC4800 Modem
Action
IRQ
EN
, INVSYM, and
28
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Reset the device and start searching for a Frame
Sync pattern using AFSD.
AFSD should always be used instead of SFS to
look for the first Frame Sync when switching into
Rx mode or when the Rx channel is changed.
AFSDET will go to 1 when Frame Sync is
detected.
Tell the CMX969 to receive and decode the first
Header block.
Keep AFSD function running in case a false
Frame Sync had been detected or in case a new
transmitter starts up on this radio channel.
Wait for the CMX969 to finish the current task or
for the AFSD function to recognize a new Frame
Sync.
If a new Frame Sync has been detected then it is
the start of a new message so abandon the ‘old’
one and start to receive and decode the ‘new’
one.
CMX969 has received and decoded a Header,
Intermediate, or Last block. Read the data and
check the CRC if the block contained one.
If we want to continue receiving the rest of this Rx
message then tell the CMX969 to receive and
decode the next block. Keep the AFSD function
running in case a new transmitter starts up on this
channel (SFR)
AFSD will detect the next Frame Sync pattern.
See Note.
Description
CMX969 Advance Information
Doc. # 20480211.002