OXCFU950_07 Datasheet, PDF (54/74 Pages) Oxford Semiconductor – USB/UART multi-function 16-bit PC Card device

OXFORD SEMICONDUCTOR, INC.
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.
8.9.2 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] is set and a level 5 interrupt is asserted, if
enabled by IER[5]. This flag is 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.
8.9.3 Automatic In-band Flow Control
When in-band receive flow control is enabled, the UART
compares the received data with Xoff1 or Xoff2 characters
to detect an Xoff condition. When this occurs, the UART
disables transmission as soon as any current character
transmission is complete. Status bits ISR[4] and ASR[0]
are set. A level 5 interrupt occurs, if enabled by IER[5]. The
UART then compares all received data with Xon1 or Xon2
characters to detect an Xon condition. When this occurs,
the UART re-enables transmission and status bits ISR[4]
and ASR[0] are cleared.
Any valid Xon/Xoff characters are not written into the RHR,
apart from when special character detection is enabled and
an Xoff2 character is received that is a valid Xoff. In this
instance, the character is 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.
When the Xon-Any flag (MCR[5]) is set, any received
character is accepted as a valid Xon condition and the
transmitter is re-enabled. The received data is transferred
to the RHR.
OXCFU950 DATA SHEET
When in-band transmit flow control is enabled, the RFL is
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
is sent and ASR[1] is set. If ASR[1] is set and the RFL falls
below the lower trigger level, Xon is sent and ASR[1] is
cleared.
If transmit flow control is disabled after an Xoff has been
sent, an Xon is sent automatically.
8.9.4 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. In non-enhanced mode, MCR[5]
enables both RTS and CTS flow control. In enhanced
mode, EFR[6] enables automatic RTS flow control and
EFR[7] enables automatic CTS flow control. This allows
software compatibility with both 16C654 and 16C750
drivers.
When automatic CTS flow control is enabled and the CTS#
input becomes active, the UART disables transmission as
soon as any current character transmission is complete.
Transmission is resumed whenever the CTS# input
becomes inactive.
When automatic RTS flow control is enabled, the RTS# pin
is forced inactive when the RFL reaches the upper trigger
level and returns 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.
DS-0023 February 2007
External—Free Release
Page 54 of 74