CMX969 Consumer Microcircuits Limited, CMX969 Datasheet - Page 30

• Manufacturer Part Number: CMX969
• Description: RD-LAP/MDC4800/Motient/ARDIS4-Level FSK Packet Data Modem
• Manufacturer: Consumer Microcircuits Limited

RD-LAP/MDC4800 Motient/ARDIS
1.6.2
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.
Step
2001 Consumer Microcircuits Limited
0
1
2
3
4
Switch radio onto receive channel.
CMX969 Mode Register IRQNEN, INVSYM
and 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 or 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.
Rx Control Procedure
Action
30
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 fist 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 recognise a new
Frame Sync.
If a new Frame Sync has been detected then it
is the start of a new message to 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.
Notes
CMX969
D/969/5