CMX644AD2 View Datasheet(PDF) - MX-COM Inc
Part Name
Description
MFG CO.
'CMX644AD2' PDF : 31 Pages View PDF
Bell 212A / V.22 Modem with Call Progress and DTMF
24
CMX644A Preliminary Information
5.5 Handling Underflow and Overflow Conditions
If the RX DATA BYTE Register has not been read before the next byte of Rx data is received, then the RX
DATA OVERFLOW flag will be set and the RX DATA BYTE Register will hold the most recent byte of
received data. The RX DATA READY flag will remain set if the FLAGS Register is not read before the
overflow condition occurs. Both RX DATA READY and RX DATA OVERFLOW flags are reset upon reading
the FLAGS Register, and are not set again until after the RX DATA BYTE Register has been read (i.e. the
overflow condition has been cleared).
If the TX DATA BYTE Register is not written to before the last byte of Tx data is sent, then the TX DATA
UNDERFLOW flag will be set and the Tx data will then consist of continuous mark ("1"), which will normally
be scrambled, until new data is loaded into the TX DATA BYTE Register. The TX DATA READY flag will
remain set if the FLAGS Register is not read before the underflow condition occurs. Both TX DATA READY
and TX DATA UNDERFLOW flags are reset upon reading the FLAGS Register, and are not set again until
after the TX DATA BYTE Register has been loaded with new data (i.e. the underflow condition has been
cleared).
C-BUS transactions to handle underflow and overflow conditions are shown in the timing diagram of Figure
13. Note that allowance should be made for C-BUS latency (TDEL and TLOAD) when changing register
settings. e.g. To change the number of Tx stop bits transmitted with all subsequent data (STOP BITS A and
B), first wait until the TX DATA READY flag is set. If this check is not made, then the number of stop bits in
the Tx data byte that is currently being sent will be changed.
2000 MX-COM, Inc.
www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054
Doc. # 20480197.006
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.
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