Serial Line Control Register (Lcr N ) - Intel 386 User Manual

11.3.6 Serial Line Control Register (LCR n )

Use LCRn to provide access to the multiplexed registers, send a break condition, and determine
the data frame for receptions and transmissions.
Serial Line Control
LCR0, LCR1
(read/write)
7
DLAB SB
Bit Bit
Number Mnemonic
7 DLAB
6 SB
5 SP
4 EPS
3 PEN
2 STB
1–0 WLS1:0
Figure 11-15. Serial Line Control Register (LCR n )
SP EPS
Divisor Latch Access Bit:
This bit determines which of the multiplexed registers is accessed.
0 = Allows access to the receiver and transmit buffer registers (RBR n and
TBR n ) and the interrupt enable register (IER n ).
1 = Allows access to the divisor latch registers (DLL n and DLH n ).
Set Break:
0 = No effect on TXD n .
1 = Forces the TXD n pin to the spacing (logic 0) state for as long as bit is
set.
Sticky Parity, Even Parity Select, and Parity Enable:
These bits determine whether the control logic produces (during
transmission) or checks for (during reception) even, odd, no, or forced
parity.
SP EPS PEN Function
X X 0 parity disabled (no parity option)
0 0 1 produce or check for odd parity
0 1 1 produce or check for even parity
1 0 1 produce or check for forced parity (parity bit = 1)
1 1 1 produce or check for forced parity (parity bit = 0)
Stop Bits:
This bit specifies the number of stop bits transmitted and received in each
serial character.
0 = 1 stop bit
1 = 2 stop bits (1.5 stop bits for 5-bit characters)
Word Length Select:
These bits specify the number of data bits in each transmitted or received
serial character.
00 = 5-bit character
01 = 6-bit character
10 = 7-bit character
11 = 8-bit character
ASYNCHRONOUS SERIAL I/O UNIT
LCR0
Expanded Addr: F4FBH
ISA Addr: 03FBH
Reset State: 00H
PEN STB WLS1
Function
LCR1
F8FBH
02FBH
00H
0
WLS0
11-25