
W83977ATF
PRELIMINARY
Publication Release Date: April 1998
-10-
Revision 0.52
1.3 Serial Port Interface
SYMBOL
PIN
41
48
I/O
IN
t
FUNCTION
CTSA
CTSB
Clear To Send. This is the modem control input.
The function of these pins can be tested by reading bit 4 of the
handshake status register.
Data Set Ready. An active low signal indicates the modem or
data set is ready to establish a communication link and transfer
data to the UART.
UART A Request To Send. An active low signal informs the
modem or data set that the controller is ready to send data.
DSRA
DSRB
42
49
IN
t
RTSA
43
I/O
8t
HEFRAS
During power-on reset, this pin is pulled down internally and is
defined as HEFRAS, which provides the power-on value for
CR26 bit 6 (HEFRAS). A 4.7 k
is recommended if intends to
pull up. (select 370H as configuration I/O port
′
s address)
UART B Request To Send. An active low signal informs the
modem or data set that the controller is ready to send data.
UART A Data Terminal Ready. An active low signal informs the
modem or data set that the controller is ready to communicate.
During power-on reset, this pin is pulled down internally and is
defined as PNPCSV , which provides the power-on value for
CR24 bit 0 (PNPCSV ). A 4.7 k
is recommended if intends to
pull up. (clear the default value of FDC, UARTs, and PRT)
UART B Data Terminal Ready. An active low signal informs the
modem or data set that controller is ready to communicate.
RTSB
50
I/O
8t
DTRA
PNPCSV
44
I/O
8t
DTRB
51
I/O
8t
SINA
SINB
SOUTA
45, 52
IN
t
Serial Input. It is used to receive serial data through the
communication link.
UART A Serial Output. It is used to transmit serial data out to the
communication link.
46
I/O
8t
PENKBC
During power-on reset, this pin is pulled down internally and is
defined as PENKBC, which provides the power-on value for
CR24 bit 2 (ENKBC). A 4.7 k
resistor is recommended if
intends to pull up. (enable KBC)
UART B Serial Output. During power-on reset, this pin is pulled
down internally and is defined as
PEN48
, which provides the
power-on value for CR24 bit 6 (
EN48
). A 4.7 k
resistor is
recommended if intends to pull up.
Data Carrier Detect. An active low signal indicates the modem
or data set has detected a data carrier.
SOUTB
PEN48
53
I/O
8t
DCDA
DCDB
47
54
65
66
IN
t
RIA
RIB
IN
t
Ring Indicator. An active low signal indicates that a ring signal is
being received from the modem or data set.