pc87311a National Semiconductor Corporation, pc87311a Datasheet - Page 50

• Manufacturer Part Number: pc87311a
• Description: Pc87311a/pc87312 Superi/otm Ii/iii Floppy Disk Controller With Dual Uarts, Parallel Port, And Ide Interface
• Manufacturer: National Semiconductor Corporation

6 0 Serial Ports
Note 1 Boldface bits are permanently low
Note 2 Bits 7–4 are driven by the input signals
Bit 4
Bit 5
Bit 6
Interrupt Enable Register
Interrupt Identification Register
Line Control Register
MODEM Control Register
Line Status Register
MODEM Status Register
SOUT
INTR (RCVR Errs)
INTR (RCVR Data Ready)
INTR (THRE)
INTR (Modem Status Changes)
Interrupt Enable Bit
RTS
DTR
This bit is the Even Parity Select bit When parity is
enabled and bit 4 is a logic 0 an odd number of
logic 1s is transmitted or checked in the data word
bits and Parity bit When parity is enabled and bit 4
is a logic 1 an even number of logic 1s is transmit-
ted or checked
This bit is the Stick Parity bit When parity is en-
abled it is used in conjunction with bit 4 to select
Mark or Space Parity When LCR bits 3 4 and 5
are logic 1 the Parity bit is transmitted and
checked as a logic 0 (Space Parity) If bits 3 and 5
are 1 and bit 4 is a logic 0 then the Parity bit is
transmitted and checked as a logic 1 (Mark Pari-
ty) If bit 5 is a logic 0 Stick Parity is disabled
This bit is the Break Control bit It causes a break
condition to be transmitted to the receiving UART
When it is set to a logic 1 the serial output (SOUT)
is forced to the Spacing state (logic 0) The break
is disabled by setting bit 6 to a logic 0 The Break
Register
l
Signal
(Continued)
TABLE 6-3 PC87311A UART Reset Configuration
Master Reset
Master Reset
Master Reset
Master Reset
Master Reset
Master Reset
Master Reset
Read LSR
Read RBR
Read IIR
Read MSR
Master Reset
Master Reset
Master Reset
Reset Control
50
l
Write THR
l
l
l
MR
Bit 7
MR
MR
l
Control bit acts only on SOUT and has no effect
on the transmitter logic
Note This feature enables the CPU to alert a terminal If the
1 Wait for the transmitter to be idle (TEMT
2 Set break for the appropriate amount of time If
3 Clear break when normal transmission has to
During the break the Transmitter can be used as
a character timer to accurately establish the break
duration by sending characters and monitoring
THRE and TEMT
This bit is the Divisor Latch Access Bit (DLAB) It
must be set high (logic 1) to access the Divisor
Latches of the Baud rate Generator during a Read
or Write operation or to have the BOUT signal ap-
pear on the BOUT pin It must be set low (logic 0)
to access any other register
MR
the transmitter will be used to time the break
duration then check that TEMT
clearing the Break Control bit
be restored
following sequence is used no erroneous characters will
be transmitted because of the break
0000 0000 (Note 1)
0000 0001
0000 0000
0000 0000
0110 0000
XXXX 0000 (Note 2)
High
Low TRI-STATE
Low TRI-STATE
Low TRI-STATE
Low TRI-STATE
Low
High
High
Reset State
e
1 before
e
1)