ST16C454
18
Rev. 3.31
at the top of the RHR.
LSR BIT-3:
Logic 0 = No framing error. (normal default condition)
Logic 1 = Framing error. The receive character did not
have a valid stop bit(s).
LSR BIT-4:
Logic 0 = No break condition. (normal default condi-
tion)
Logic 1 = The receiver received a break signal (RX
was a logic 0 for one character frame time).
LSR BIT-5:
This bit indicates that the 454 is ready to accept new
characters for transmission. This bit causes the 454 to
issue an interrupt to the CPU when the transmit
holding register is empty and the interrupt enable is
set.
Logic 0 = Transmit holding register is not empty.
(normal default condition)
Logic 1 = Transmit holding register is empty.
LSR BIT-6:
Logic 0 = Transmitter holding and shift registers are
full.
Logic 1 = Transmitter holding and shift registers are
empty (normal default condition).
LSR BIT-7:
Not used - Initialized to a logic 0.
Modem Status Register (MSR)
This register provides the current state of the control
interface signals from the modem, or other peripheral
device that the 454 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 454 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 454 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 454 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 has
changed state since the last time it was read. A
modem Status Interrupt will be generated.
MSR BIT-4:
-CTS (active high, logical 1). 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 ST16C454 provides a temporary data register to
store 8 bits of user information.
