DAN-101 Datasheet, PDF (1/3 Pages) Exar Corporation – Replacing SCN68681 with XR68C681 DUART

DATA COMMUNICATIONS APPLICATION NOTE
DAN-101
Replacing SCN68681 with XR68C681 DUART
May 1999
Description
This application note describes the major difference between the Exar XR68C681 and the Philips
SCN68681. Items noted herein must be carefully considered whenever replacing with the XR68C681
device. Check your design to see if it applies.
1.0 Software
The XR68C681 is software compatible to the Philips SCN68681. All registers are compatible and there
is no software change requirement.
2.0 Hardware
2.1 The XR68C681 is pin-to-pin compatible to the SCN68681 in the following packages:
XR68C681CJ = SCN68681C1A44 ; commercial temperature
XR68C681J = SCN68681E1A44 ; industrial temperature
XR68C681CP = SCN68681C1N40 ; commercial temperature
XR68C681P = SCN68681E1N40 ; industrial temperature
XR68C681N = SCN68681E1F40 ; ceramic package and industrial temperature
2.2 The XR68C681 is fabricated in low power CMOS process and the SCN68681 is made in NMOS
process. The XR68C681 consumes 10 times less power than SCN68681.
Icc
Typical
Maximum
XR68C681
6mA
15mA
SCN68681
n.a
150-175mA
2.3 The oscillator circuit on X1 and X2 pins is different and depending upon application environment it may
or may not be compatible, refer to figure 1 on the next page. Figure 1 shows 3 applications that will
need to be considered in the review process. The oscillator circuit and connection for SCN68681 is
exhibited in the second column and the circuit for XR68C681 is shown under the third column. As it is
illustrated, the internal inverter for the oscillator circuit is reversed. Hence, the XR68C681 is compatible
under application #1 and should work fine. However, application #2 and #3 must be carefully reviewed
by the designer.
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