NS16C552 Datasheet, PDF (13/24 Pages) Texas Instruments – PC16552D Dual Universal Asynchronous Receiver/Transmitter with FIFOs†

6 0 Pin Descriptions (Continued)
RI1 RI2 (Ring Indicator) pins 43 31 When low this indi-
cates that a telephone ringing signal has been received by
the MODEM or data set The RI signal is a MODEM status
input whose condition the CPU can test by reading bit 6 (RI)
of the MODEM Status Register for the appropriate channel
Bit 6 is the complement of the RI signal Bit 2 (TERI) of the
MODEM Status Register indicates whether the RI input sig-
nal has changed from a low to a high state since the previ-
ous reading of the MODEM Status Register
Note Whenever the RI bit of the MODEM Status Register changes from a
high to a low state an interrupt is generated if the MODEM Status
Interrupt is enabled
SIN1 SIN2 (Serial Input) pins 39 25 Serial data input from
the communications link (peripheral device MODEM or
data set)
SOUT1 SOUT2 (Serial Output) pins 38 26 Composite se-
rial data output to the communications link (peripheral
MODEM or data set) The SOUT signal is set to the Marking
(logic 1) state upon a Master Reset operation
TXRDY1 TXRDY2 (Transmitter Ready) pins 1 32 Trans-
mitter DMA signalling is available through two pins When
operating in the FIFO mode the CPU selects one of
two types of DMA transfer via FCR3 When operating as in
the 16450 Mode only DMA mode 0 is allowed Mode 0
supports single transfer DMA where a transfer is made be-
tween CPU bus cycles Mode 1 supports multi-transfer DMA
where multiple transfers are made continuously until the
XMIT FIFO has been filled Details regarding the active and
inactive states of this signal are given in Section 8 5 Bit 3
V_DD (Power) pins 33 44 a5V Supply
V_SS (Ground) pins 12 22 0V Reference
WR (Write) pin 20 When WR is low while the chip is select-
ed the CPU can write control words or data into the select-
ed DUART register
XIN (External Crystal Input) pin 11 This signal input is used
in conjunction with XOUT to form a feedback circuit for the
baud rate generator’s oscillator If a clock signal will be gen-
erated off-chip then it should drive the baud rate generator
through this pin
XOUT (External Crystal Output) pin 13 This signal output is
used in conjunction with XIN to form a feedback circuit for
the baud rate generator’s oscillator If the clock signal will
be generated off-chip then this pin is unused
7 0 Connection Diagram
Chip Carrier Package
Top View
Order Number PC16552D
See NS Package Number V44A
TL C 9426 – 17
12