OX16C950 rev B
OXFORD SEMICONDUCTOR LTD.
EFR[6]: Enable automatic RTS flow control.
logic 0 ⇒ RTS flow control is disabled (default).
logic 1 ⇒ RTS flow control is enabled in Enhanced mode
(i.e. EFR[4] = 1), where the RTS# pin will be
forced inactive high if the RFL reaches the
upper flow control threshold. This will be
released when the RFL drops below the lower
threshold. The 650 and 950 software drivers
should use this bit to enable RTS flow control.
The 750 compatible driver uses MCR[5] to
enable RTS flow control.
When the 'XON Any' flag (MCR[5]) is set, any received
character is accepted as a valid XON condition and the
transmitter will be re-enabled. The received data will be
transferred to the RHR.
When in-band transmit flow control is enabled, the RFL will
be sampled whenever the transmitter is idle (briefly,
between characters, or when the THR is empty) and an
XON/XOFF character may be inserted into the data stream
if needed. Initially, remote transmissions are enabled and
hence ASR[1] is clear. If ASR[1] is clear and the RFL has
passed the upper trigger level (i.e. is above the trigger
level), XOFF will be sent and ASR[1] will be set. If ASR[1]
is set and the RFL falls below the lower trigger level, XON
will be sent and ASR[1] will be cleared.
EFR[7]: Enable automatic CTS flow control.
logic 0 ⇒ CTS flow control is disabled (default).
logic 1 ⇒ CTS flow control is enabled in Enhanced mode
(i.e. EFR[4] = 1), where the data transmission
is prevented whenever the CTS# pin is held
inactive high. The 650 and 950 software
drivers should use this bit to enable CTS flow
control. The 750 compatible driver uses
MCR[5] to enable CTS flow control.
If transmit flow control is disabled after an XOFF has been
sent, an XON will be sent automatically.
13.4 Automatic Out-of-band Flow Control
Automatic RTS/CTS flow control is selected by different
means, depending on whether the UART is in Enhanced or
non-Enhanced mode. When in non-Enhanced mode,
MCR[5] enables both RTS and CTS flow control. When in
Enhanced mode, EFR[6] enables automatic RTS flow
control and EFR[7] enables automatic CTS flow control.
This allows software compatibility with both 16C650 and
16C750 drivers.
13.2 Special Character Detection
In Enhanced mode (EFR[4]=1), when special character
detection is enabled (EFR[5]=1) and the receiver matches
received data with XOFF2, the 'received special character'
flag ASR[4] will be set and a level 5 interrupt is asserted, (if
enabled by IER[5]). This flag will be cleared following a
read of ASR. The received status (i.e. parity and framing)
of special characters does not have to be valid for these
characters to be accepted as valid matches.
When automatic CTS flow control is enabled and the CTS#
input becomes active, the UART will disable transmission
as soon as any current character transmission is complete.
Transmission is resumed whenever the CTS# input
becomes inactive.
13.3 Automatic In-band Flow Control
When in-band receive flow control is enabled, the UART
will compare the received data with XOFF1 or XOFF2
characters to detect an XOFF condition. When this occurs,
the UART will disable transmission as soon as any current
character transmission is complete. Status bits ISR[4] and
ASR[0] will be set. A level 5 interrupt will occur if enabled
by IER[5]. The UART will then compare all received data
with XON1 or XON2 characters to detect an XON
condition. When this occurs, the UART will re-enable
transmission and status bits ISR[4] and ASR[0] will be
cleared.
When automatic RTS flow control is enabled, the RTS# pin
will be forced inactive when the RFL reaches the upper
trigger level and will return to active when the RFL falls
below the lower trigger level. The automatic RTS# flow
control is ANDed with MCR[1] and hence is only
operational when MCR[1]=1. This allows the software
driver to override the automatic flow control and disable the
remote transmitter regardless by setting MCR[1]=0 at any
time.
Automatic DTR/DSR flow control behaves in the same
manner as RTS/CTS flow control but is enabled by
ACR[3:2], regardless of whether or not the UART is in
Enhanced mode.
Any valid XON/XOFF characters will not be written into the
RHR. An exception to this rule occurs if special character
detection is enabled and an XOFF2 character is received
that is a valid XOFF. In this instance, the character will be
written into the RHR.
The received status (i.e. parity and framing) of XON/XOFF
characters does not have to be valid for these characters to
be accepted as valid matches.
Data Sheet Revision 1.2
Page 29
OXFORD [ OXFORD SEMICONDUCTOR ]
