DAN-133 Datasheet, PDF (1/8 Pages) Exar Corporation – EXAR’S QUARTS COMPARED

DATA COMMUNICATIONS APPLICATION NOTE
DAN133
June 2002
EXAR’S QUARTS COMPARED WITH TI’S TL16C554 AND TL16C554A
Author: PY
1.0 INTRODUCTION
This application note describes the major difference between Exar’s QUARTs (ST16C554, ST16C654, and
XR16C854) with TI’s TL16C554 and TL16C554A. These devices are similar, with a few hardware, bus timing
and firmware-related differences.
1.1 TL16C554 AND TL16C554A
The TL16C554 is listed by TI as “not recommended for new designs.” In its place, they recommend the
TL16C554A. The TL16C554A is an enhanced version of the TL16C554 that can operate at 5 V and 3.3 V and
has Automatic RTS/CTS Flow Control.
1.2 HARDWARE DIFFERENCES
• The TI TL16C554A and Exar’s ST16C554, ST16C654 and XR16C854 are all available in the 68-pin PLCC
package. The Exar QUARTs are also available in the 64-pin TQFP and 100-pin QFP package while the TI
QUARTs are available in a 80-pin QFP package. The Exar and TI QUARTs are pin-to-pin compatible in the
68-pin PLCC package.
• The oscillator circuitry is similar and will operate in most cases, but there are some differences when using a
crystal oscillator and when using an external clock. See Figure 1below for the differences in the oscillator
circuitry for a crystal oscillator. When using an external clock input for frequencies greater than 24 MHz, the
Exar QUARTs will require a 2K pull-up resistor on the XTAL2 pin.
FIGURE 1. CRYSTAL OSCILLATOR CIRCUITRY DIFFERENCES
TL16C554A
Exar QUART
XTAL1
C1
10-30 pF
XTAL2
R2
1 ΜΩ
Y1
C2
40-60 pF
R1
1.5 KΩ
1.8432
MHz
to
16
MHz
XTAL1
XTAL2
R2
500 ΚΩ − 1 ΜΩ
Y1
C1
22-47 pF
C2
22-47 pF
R1
0-120 Ω
(Optional)
1.8432
MHz
to
24
MHz
EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com • [e-mail]