scn68681 NXP Semiconductors, scn68681 Datasheet - Page 21

• Manufacturer Part Number: scn68681
• Description: Dual Asynchronous Receiver/transmitter Duart
• Manufacturer: NXP Semiconductors

Philips Semiconductors
2004 Mar 02
NOTES:
1. INTRN or OP3 – OP7 when used as interrupt outputs.
2. The test for open drain outputs is intended to guarantee switching of the output transistor. Measurement of this response is referenced from the mid point of the switching signal, V
X1/CLK
When using an external clock it is preferred to drive X2 and leave X1 open.
X2 is the input to the internal driver, while X1 is the output.
R1 is only required if U1 will not drive to X2 high level.
Previous specifications indicated X2 should be grounded and X1
should be driven. This is still acceptable. It is electrically easier to drive
the amplifier input than to overdrive its output.
CTCLK
Dual asynchronous receiver/transmitter (DUART)
a point 0.5 volts above V
pronounced and can greatly affect the resultant measurement.
RxC
TxC
t
t
t
t
CLK
CTC
Rx
Tx
OL
. This point represents noise margin that assures true switching has occurred. Beyond this level, the effects of external circuitry and test environment are
(1X OUTPUT)
(INPUT)
t
t
t
t
CLK
CTC
Rx
Tx
TxC
TxC
TxD
INTERRUPT
(READ OR
OUTPUT
WRITE)
EXTERNAL SOURCE
CSN
Figure 10. Interrupt Timing
Figure 11. Transmit Timing
DRIVING FROM
Figure 9. Clock Timing
1
t
TXD
(1 OR 16 CLOCKS)
U1
1 BIT TIME
t
TCS
OPEN
1K
21
+5V
R1
X2
V
X1
t
M
IR
CRYSTAL SERIES RESISTANCE3 SHOULD BE LESS THAN 180
C2
C1
V
OL
V
R1: 100K - 1Meg (See design note)
+0.5V
C1 = C2: 0-5pF + (STRAY < 5pF)
OL
3.6864MHz
R2 = 50k to 150k
SD00117
X1
X2
R2
SCN2681
74LS04
SCN68681
1K
+5V
OF THE DUART
TO THE REST
CIRCUITS
Product data
SD00115
TO OTHER
CLOCK
CHIPS
SD00116
M
, to