11-15
ASYNCHRONOUS SERIAL I/O UNIT
11.3 REGISTER DEFINITIONSTable 11-5 lists the registers associated with the SIO unit and the following sections contain bitdescriptions for each register.

Table 11-5. SIO Registers(Sheet 1 of 2)

Register Expanded
Address PC/AT*
Address Function
PINCFG
(read/write) 0F826H — Pin Configuration:
Connects the SIO1 transmit data (TXD1), data terminal ready
(DTR1#), and request to send (RTS1#) signals to package pins.
P1CFG
(read/write) 0F820H — Port 1 Configuratio n:
Connects the SIO0 ring indicator (RI0#), data set ready (DSR0#),
data terminal ready (DTR0#), request to send (RTS0#), and data
carrier detected (DCD0#) signals to package pins.
P2CFG
(read/write) 0F822H — Port 2 Configuratio n:
Connects the SIO0 clear to send (CTS0#), tr ansmit data (TXD0),
and receive data (RXD0) signals to package pins.
P3CFG
(read/write) 0F824H — Port 3 Configuratio n:
Connects COMCLK to the package pin.
SIOCFG
(read/write) 0F836H — SIO and SSIO Configuration:
Connects the SIO
n
modem input signals in ternally or to package
pins and connects either the internal SERCL K signal or the
COMCLK pin to the S IO
n
baud-rate generator in put.
DLL0
DLL1
(read/write)
0F4F8H
0F8F8H 03F8H
02F8H Divisor Latch Low:
Stores the lower 8 bits of the SIO
n
baud-rate generator divisor.
DLH0
DLH1
(read/write)
0F4F9H
0F8F9H 03F9H
02F9H Divisor Latch High:
Stores the upper 8 b its of the SIO
n
baud-rate generator divisor.
TBR0
TBR1
(write only)
0F4F8H
0F8F8H 03F8H
02F8H Transmit Buffer:
Holds the data byte to transmit.
RBR0
RBR1
(read only)
0F4F8H
0F8F8H 03F8H
02F8H Receiver Buffer:
Holds the data byte received.
LCR0
LCR1
(read/write)
0F4FBH
0F8FBH 03FBH
02FBH Line Control:
Specifies the data frame (word length, number of stop bits, and
type of parity) for transmissions and re ceptions. Allows the
transmitter to transmit a break condition.
LSR0
LSR1
(read only)
0F4FDH
0F8FDH 03FDH
02FDH Line Status:
Contains the transmitter empty, transmit b uffer empty, receive
buffer full, and receive error fl ags.
IER0
IER1
(read/write)
0F4F9H
0F8F9H 03F9H
02F9H Interrupt Enable:
Independently connects the four signals (modem status, receive
line status, transmit buffer e mpty, and receive buffer full) to the
interrupt request output (SIOINT
n
).