OX16C950 rev B
OXFORD SEMICONDUCTOR LTD.
13 AUTOMATIC FLOW CONTROL
Automatic in-band flow control, automatic out-of-band flow
control and special character detection features can be
used when in Enhanced mode and are software compatible
with the 16C654. Alternatively, 16C750 compatible
automatic out-of-band flow control can be enabled when in
non-Enhanced mode. In 950 mode, in-band and out-of-
band flow controls are compatible with 16C654, with the
addition of fully programmable flow control thresholds.
EFR[3:2]: In-band transmit flow control mode
When in-band transmit flow control is enabled, an
XON/XOFF character is inserted into the data stream
whenever the RFL passes the upper trigger level and falls
below the lower trigger level respectively.
For automatic in-band flow control, bit 4 of EFR must be
set. The combinations of software transmit flow control can
then be selected by programming EFR[3:2] as follows:
13.1 Enhanced Features Register ‘EFR’
logic [00] ⇒ In-band transmit flow control is disabled.
logic [01] ⇒ Single character in-band transmit flow
control enabled, using XON2 as the XON
character and XOFF2 as the XOFF
character.
logic [10] ⇒ Single character in-band transmit flow
control enabled, using XON1 as the XON
character and XOFF1 as the XOFF
character.
Writing 0xBF to LCR enables access to the EFR and other
Enhanced mode registers. This value corresponds to an
unused data format. Writing 0xBF to LCR will set LCR[7]
but leaves LCR[6:0] unchanged. Therefore, the data format
of the transmitter and receiver data is not affected. Write
the desired LCR value to exit from this selection.
Note: In-band transmit and receive flow control is disabled
in 9-bit mode.
Logic[11] ⇒ The value EFR[3:2] = “11” is reserved for
future use and should not be used
EFR[1:0]: In-band receive flow control mode
When in-band receive flow control is enabled, the UART
compares the received data with the programmed XOFF
character. When this occurs, the UART will disable
transmission as soon as any current character
transmission is complete. The UART then compares the
received data with the programmed XON character. When
a match occurs, the UART will re-enable transmission (see
section 15.6).
EFR[4]: Enhanced mode
logic 0 ⇒ Non-Enhanced mode. Disables IER bits 4-7,
ISR bits 4-5, FCR bits 4-5, MCR bits 5-7 and
in-band flow control. Whenever this bit is
cleared, the setting of other bits of EFR are
ignored.
logic 1 ⇒ Enhanced mode. Enables the Enhanced Mode
functions. These functions include enabling
IER bits 4-7, FCR bits 4-5, MCR bits 5-7. For
in-band flow control the software driver must
set this bit first. If this bit is set, out-of-band
flow control is configured with EFR bits 6-7,
otherwise out-of-band flow control is
compatible with 16C750.
For automatic in-band flow control, bit 4 of EFR must be
set. The combinations of software receive flow control can
be selected by programming EFR[1:0] as follows:
logic [00] ⇒ In-band receive flow control is disabled.
logic [01] ⇒ Single character in-band receive flow control
enabled, recognising XON2 as the XON
character and XOFF2 as the XOFF
character.
logic [10] ⇒ Single character in-band receive flow control
enabled, recognising XON1 as the XON
character and XOFF1 and the XOFF
character.
logic [11] ⇒ The behavior of the receive flow control is
dependent on the configuration of EFR[3:2].
single character in-band receive flow control
is enabled, accepting both XON1 and XON2
as valid XON characters and both XOFF1
and XOFF2 as valid XOFF characters when
EFR[3:2] = “01” or “10”. EFR[1:0] should not
be set to “11” when EFR[3:2] is either “00”.
EFR[5]: Enable special character detection
logic 0 ⇒ Special character detection is disabled.
logic 1 ⇒ While in Enhanced mode (EFR[4]=1), the
UART compares the incoming receiver data
with the XOFF2 value. Upon a correct match,
the received data will be transferred to the
RHR and a level 5 interrupt (XOFF or special
character) will be asserted if level 5 interrupts
are enabled (IER[5] set to 1).
Data Sheet Revision 1.2
Page 28
OXFORD [ OXFORD SEMICONDUCTOR ]
