PEB 20532
PEF 20532
Detailed Protocol Description
Data Sheet
99
2000-09-14
In-Band Flow Control of Transmitted Characters:
Recognition of an XON or XOFF character causes always a corresponding maskable
interrupt status to be generated.
Further action depends on the setting of control bit
’
FLON
’
(Flow Control On) in register
CCR2H
:
0: No further action is automatically taken by the SCC.
1: The reception of an XOFF character automatically turns off the transmitter after the
currently transmitted character (if any) has been shifted out completely (entering
XOFF state). The reception of an XON character automatically makes the transmitter
resume transmitting (entering XON state).
After hardware RESET, bit
CCR2H
:FLON is
‘
0
’
.
When bit
CCR2H
:FLON is programmed from
‘
0
’
to
‘
1
’
, the transmitter is first in the
‘
XON state
’
, until an XOFF character is received.
When bit
CCR2H
:FLON is programmed from
‘
1
’
to
‘
0
’
, the transmitter always goes in the
‘
XON state
’
, and transmission is only controlled by the user and by the CTS signal input.
The in-band flow control of the transmitter via received XON and XOFF characters can
be combined with control via CTS pin, i.e. the effect of the CTS pin is independent of
whether in-band control is used or not. The transmitter is enabled only if CTS is
‘
low
’
and
XON state has been reached.
Transmitter Status Bit:
The status bit
‘
Flow Control Status
’
(bit
’
FCS
’
in register
STARL
) indicates the current
state of the transmitter, as follows:
0: if the transmitter is in XON state,
1: if the transmitter is in XOFF state.
Note: The transmitter cannot be turned off by software without disrupting data possibly
remaining in the transmit FIFO.
Flow Control for Received Data:
After writing a character value to register
TICR
(Transmit Immediate Character,
’
TIC
’
) its
character contents is inserted into the outgoing character stream
immediately upon writing this register by the microprocessor if the transmitter is in
IDLE state. If no further characters (transmit FIFO empty) are to be transmitted, i.e.
the transmitter returns to IDLE state after transmission of the
’
TIC
’
and an ALLS (All
Sent) interrupt will be generated.
after the end of a character currently being transmitted if the transmitter is not in IDLE
state. This does not affect the contents of the transmit FIFO. Transmission of
characters from transmit FIFO is resumed after the
’
TIC
’
is send out.