
PEB 20542
PEF 20542
Detailed Protocol Description
Data Sheet
102
2000-09-14
Additionally, the CTS signal may be used to control data transmission.
4.4.4
Special Functions
4.4.4.1
Break Detection/Generation
Break generation:
On issuing the transmit break command (bit
’
XBRK
’
in register
CCR3L
), the TxD pin is
immediately forced to physical
‘
0
’
level with the next following transmit clock edge, and
released with the first transmit clock edge after this command is reset again by software.
Break detection:
The SCC recognizes the break condition upon receiving consecutive (physical)
‘
0
’
s for
the defined character length, the optional parity and the selected number of stop bits
(
‘
zero
’
character and framing error). The
‘
zero
’
character is not pushed to RFIFO. If
enabled, the
’
Break
’
interrupt (BRK) is generated.
The break condition will be present until a
‘
1
’
is received which is indicated by the
‘
Break
Terminated
’
interrupt (BRKT).
4.4.4.2
In-band Flow Control by XON/XOFF Characters
Programmable XON and XOFF characters:
The
XON
/
XOFF
registers contain the programmable values for XON and XOFF
characters. The number of significant bits in a register is determined by the programmed
character length via bit field
’
CHL
’
in register
CCR3L
.
Additionally, two programmable eight-bit values in registers
MXON
and
MXOFF
serve
as masks for the characters XON and XOFF, respectively:
A
‘
1
’
in any mask bit position has the effect that no comparison is performed between the
corresponding bits in the received characters (
‘
don
’
t cares
’
) and the XON/XOFF value.
At RESET, the masks are zero
’
ed, i.e. all bit positions will be compared.
A received character is considered to be recognized as a valid XON or XOFF character
–
if it is correctly framed (correct length),
–
if its bits match the ones in the
XON
or
XOFF
registers over the programmed character
length,
–
if it has correct parity (if applicable).
Received XON and XOFF characters are stored in the SCC receive FIFO, as any other
characters, when bit
’
DXS
’
is set to
’
0
’
in register
CCR3L
. Otherwise they are not stored
in the receive FIFO.