RC56D, RC336D, and RC144D Modem Device Sets Designer’s Guide
4-6
Conexant
1154
4.2.4 LCR - Line Control Register (Addr = 3)
The Line Control Register (LCR) specifies the format of the asynchronous data communications exchange.
Bit 7
Divisor Latch Access Bit (DLAB).
This bit must be set to a 1 to access the Divisor latch registers during a read or write operation. It must be
reset to a 0 to access the Receiver Buffer, the Transmitter Buffer, or the Interrupt Enable Register.
Bit 6
Set Break.
When bit 6 is a 1, the transmit data is forced to the break condition, i.e., space (0) is sent. When bit 6 is a 0,
break is not sent. The Set Break bit acts only on the transmit data and has no effect on the serial in logic.
Bit 5
Stick Parity.
When parity is enabled (LCR3 = 1) and stick parity is selected (LCR5 = 1), the parity bit is transmitted and
checked by the receiver as a 0 if even parity is selected (LCR4 = 1) or as a 1 if odd parity is selected (LCR4 =
0). When stick parity is not selected (LCR3 = 0), parity is transmit and checked as determined by the LCR3
and LCR4 bits.
Bit 4
Even Parity Select (EPS).
When parity is enabled (LCR3 = 1) and stick parity is not selected (LCR5 = 0), the number of 1s transmitted or
checked by the receiver in the data word bits and parity bit is either even (LCR4 = 1) or odd (LCR4 = 0).
Bit 3
Enable Parity (PEN).
When bit 3 is a 1, a parity bit is generated in the serial out (transmit) data stream and checked in the serial in
(receive) data stream as determined by the LCR 4 and LCR5 bits. The parity bit is located between the last
data bit and the first stop bit.
Bit 2
Number of Stop Bits (STB).
This bit specifies the number of stop bits in each serial out character. If bit 2 is a 0, one stop bit is generated
regardless of word length. If bit 2 is a 1 and 5-bit word length is selected, one and one-half stop bits are
generated. If bit 2 is a 1 and a 6-, 7-, or 8-bit word length is selected, two stop bits are generated. The serial in
logic checks the first stop bit only, regardless of the number of stop bits selected.
Bits 1-0
Word Length Select (WLS0 and WLS1).
These two bits specify the number of bits in each serial in or serial out character. The encoding of bits 0 and 1
is:
Bit 1
Bit 0
Word Length
0
0
5 Bits (Not supported)
0
1
6 Bits (Not supported)
1
0
7 Bits
1
1
8 Bits
Summary of Contents for RC144D
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