XR16C850 Datasheet, PDF (33/55 Pages) Exar Corporation – UART with 128-byte FIFO’s FIFO Counters and Half-duplex Control

XR16C850
Logic 1 = At least one parity error, framing error or break
indication is in the current FIFO data. This bit is cleared
when LSR register is read.
Modem Status Register (MSR)
This register provides the current state of the control
interface signals from the modem, or other peripheral
device that the 850 is connected to. Four bits of this
register are used to indicate the changed information.
These bits are set to a logic 1 whenever a control input
from the modem changes state. These bits are set to a
logic 0 whenever the CPU reads this register.
MSR BIT-0:
Logic 0 = No -CTS Change (normal default condition)
Logic 1 = The -CTS input to the 850 has changed state
since the last time it was read. A modem Status
Interrupt will be generated.
MSR BIT-1:
Logic 0 = No -DSR Change (normal default condition)
Logic 1 = The -DSR input to the 850 has changed state
since the last time it was read. A modem Status
Interrupt will be generated.
MSR BIT-2:
Logic 0 = No -RI Change (normal default condition)
Logic 1 = The -RI input to the 850 has changed from a
logic 0 to a logic 1. A modem Status Interrupt will be
generated.
MSR BIT-3:
Logic 0 = No -CD Change (normal default condition)
Logic 1 = Indicates that the -CD input to the 850 has
changed state since the last time it was read. A modem
Status Interrupt will be generated.
MSR BIT-4:
-CTS functions as hardware flow control signal input if it
is enabled via EFR bit-7. The transmit holding register
flow control is enabled/disabled by MSR bit-4. Flow
control (when enabled) allows the starting and stopping
the transmissions based on the external modem -CTS
signal. A logic 1 at the -CTS pin will stop 850 transmis-
sions as soon as current character has finished trans-
mission.
Normally MSR bit-4 bit is the compliment of the -CTS
input. However in the loop-back mode, this bit is
equivalent to the RTS bit in the MCR register.
MSR BIT-5:
DSR (active high, logical 1). Normally this bit is the
compliment of the -DSR input. In the loop-back mode,
this bit is equivalent to the DTR bit in the MCR register.
MSR BIT-6:
RI (active high, logical 1). Normally this bit is the
compliment of the -RI input. In the loop-back mode this
bit is equivalent to the OP1 bit in the MCR register.
MSR BIT-7:
CD (active high, logical 1). Normally this bit is the
compliment of the -CD input. In the loop-back mode this
bit is equivalent to the OP2 bit in the MCR register.
Scratchpad Register (SPR)
The XR16C850 provides a temporary data register to
store 8 bits of user information.
Enhanced Feature Register (EFR)
Enhanced features are enabled or disabled using this
register.
Bits-0 through 4 provide single or dual character soft-
ware flow control selection. When the Xon1 and Xon2
and/or Xoff1 and Xoff2 modes are selected (see table 7),
the double 8-bit words are concatenated into two se-
quential characters.
EFR BIT 0-3: (logic 0 or cleared is the default condition)
Combinations of software flow control can be selected
by programming these bits.
Rev. 1.20
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