
ST16C2552
18
Rev. 3.50
receiver must be programmed to check the same
format. (normal default condition)
Logic 1 = EVEN Parity
is generated by forcing an even
the number of logic 1s in the transmitted. The receiver
must be programmed to check the same format.
LCR BIT-5:
If the parity bit is enabled, LCR BIT-5 selects the
forced parity format.
LCR BIT-5 = logic 0, parity is not forced. (normal
default condition)
LCR BIT-5 = logic 1 and LCR BIT-4 = logic 0, parity bit
is forced to a logical 1 for the transmit and receive
data.
LCR BIT-5 = logic 1 and LCR BIT-4 = logic 1, parity bit
is forced to a logical 0 for the transmit and receive
data.
LCR BIT-6:
When enabled the Break control bit causes a break
condition to be transmitted (the TX output is forced to
a logic 0 state). This condition exists until disabled by
setting LCR bit-6 to a logic 0.
Logic 0 = No TX break condition. (normal default
condition)
Logic 1 = Forces the transmitter output (TX) to a logic
0 for alerting the remote receiver to a line break
condition.
LCR BIT-7:
The internal baud rate counter latch and Enhance
Feature mode enable.
Logic 0 = Divisor latch disabled. (normal default
condition)
Logic 1 = Divisor latch and enhanced feature register
enabled.
Modem Control Register (MCR)
This register controls the interface with the modem or
a peripheral device.
MCR BIT-0:
Logic 0 = Force -DTR output to a logic 1. (normal
default condition)
Logic 1 = Force -DTR output to a logic 0.
MCR BIT-1:
Logic 0 = Force -RTS output to a logic 1. (normal
default condition)
Logic 1 = Force -RTS output to a logic 0.
MCR BIT-2:
This bit is used in the Loop-back mode only. In the
loop-back mode this bit is use to write the state of the
modem -RI interface signal.
MCR BIT-3: (
Used to control the modem -CD signal in
the loop-back mode.)
Logic 0 = Forces INT (A-B) outputs to the three statte
mode and sets -OP2 to a logic 1. (normal default
condition)
In the Loop-back mode, sets -CD internally to a logic
1.
Logic 1 = Forces the INT (A-B) outputs to the active
mode and sets -OP2 to a logic 0.
In the Loop-back mode, sets -CD internally to a logic
0.
MCR BIT-4:
Enable the local loop-back mode (diagnostics). In this
mode the transmitter output (-TX) and the receiver
input (-RX), -CTS, -DSR, -CD, and -RI are discon-
nected from the 2552 I/O pins. Internally the modem
data and control pins are connected into a loop-back
data configuration. In this mode, the receiver and
transmitter interrupts remain fully operational. The
Modem Control Interrupts are also operational, but the
interrupts sources are switched to the lower four bits of
the Modem Control. Interrupts continue to be con-
trolled by the IER register.
Logic 0 = Disable loop-back mode. (normal default
condition)
Logic 1 = Enable local loop-back mode (diagnostics).
MCR BIT 5-7:
Not Used - initialized to a logic 0.
Line Status Register (LSR)
This register provides the status of data transfers
between. the 2552 and the CPU.
LSR BIT-0:
Logic 0 = No data in receive holding register or FIFO.
(normal default condition)
Logic 1 = Data has been received and is saved in the
receive holding register or FIFO.