SCN68681 Datasheet, PDF (21/28 Pages) NXP Semiconductors – Dual asynchronous receiver/transmitter DUART

Philips Semiconductors
Dual asynchronous receiver/transmitter (DUART)
Product specification
SCN68681
X1/CLK
CTCLK
RxC
TxC
t_CLK
t_CTC
t_Rx
t_Tx
t_CLK
t_CTC
t_Rx
t_Tx
DRIVING FROM
EXTERNAL SOURCE
OPEN
X1
+5V
R1: 100K - 1Meg (See design note)
C1 = C2: 0-5pF + (STRAY < 5pF)
+5V
1K
74LS04
CLOCK
TO OTHER
CHIPS
SCN2681
X1
TO THE REST
OF THE DUART
CIRCUITS
C1
R2
R1
1KΩ
C2
When using an external clock it is preferred to drive X2 and leave X1 open. _U1
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.
X2
X2
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.
3.6864MHz
CRYSTAL SERIES RESISTANCE3 SHOULD BE LESS THAN 180Ω
R2 = 50kΩ to 150kΩ
SD00115
Figure 9. Clock Timing
CSN
(READ OR
WRITE)
V_M
INTERRUPT¹
OUTPUT
t_IR
V_OL +0.5V
V_OL
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_M, to
a point 0.5 volts above V_OL. This point represents noise margin that assures true switching has occurred. Beyond this level, the effects of external circuitry and test environment are
pronounced and can greatly affect the resultant measurement.
SD00116
Figure 10. Interrupt Timing
TxC
(INPUT)
1 BIT TIME
(1 OR 16 CLOCKS)
t_TXD
TxD
TxC
(1X OUTPUT)
t_TCS
Figure 11. Transmit Timing
SD00117
1998 Sep 04
21