XR88C681_06 Datasheet, PDF (6/101 Pages) Exar Corporation – CMOS Dual Channel UART (DUART)

XR88C681
44 PLCC
30
40 PDIP,
CDIP
27
28 PDIP
31
28
32
29
20
33
30
21
34
35
31
22
36
32
23
37
33
24
Symbol
OP4
(RXRDY/
FFULL_A)
OP2
(TXCA_16)
(TXCA-1X)
(RXCA_1X)
OP0
(-RTSA)
TXDA
NC
RXDA
X1/CLK
X2
Type Description
O Output 4 (General Purpose Output). This output pin
can also be programmed to function as the open-drain,
active-low, “Receiver Ready” or “FIFO Full” indicator
output for Channel A. (-RXRDY_A/-FFULL_A)
O Output 2 (General Purpose Output). This output pin
can also be programmed to function as any of the fol-
lowing: The Channel A Transmitter 16X or 1X clock
output (TXCA_16X or TXCA_1X), or the Channel A
Receiver 1X clock output (RXCA_1X).
O Output 0 (General Purpose Output). This output pin
can also be programmed to function as the active-low,
Request-to-Send output for Channel A (-RTSA).
O Transmitter Serial Data Output (Channel A). The
least significant bit of the character is transmitted first.
This output is held in the marking (high) state when the
transmitter is idle, disabled, or operating in the Local
LOOPBACK mode. If an external transmitter clock is
specified, TXCA, the data is shifted out of the TSR
(Transmitter Shift Register) on the falling the edge of
the clock.
No Connect.
I
Receive Serial Data Input (Channel A). The least
significant bit of the character is received first. If an
external receiver clock, RXCA, is specified, the data is
sampled on the rising edge of the clock.
I
Crystal Output of External Clock Input. This pin is
the connection for one side of the crystal and a capaci-
tor to ground when the internal oscillator is used. If the
oscillator is not used, an external clock signal must be
supplied at this input.
In order for the XR88C681 device to function properly,
the user must supply a signal with frequencies be-
tween 2.0MHz and 4.0MHz. This requirement can be
met by either a crystal oscillator or by the external
TTL-compatible clock signal.
O Crystal Input. Connection for the one side of the crys-
tal (opposite of X1/CLK). If the oscillator is used, a
capacitor must also be connected from this pin to
ground. This pin must be left open if an external clock
is supplied at X1/CLK.
Rev. 2.11
6