DAN-130 Datasheet, PDF (1/11 Pages) Exar Corporation – EXAR’S DUARTS COMPARED WITH TI’S TL16C752B

DATA COMMUNICATIONS APPLICATION NOTE
DAN130
EXAR’S DUARTS COMPARED WITH TI’S TL16C752B
June 2002
Author: PY
1.0 INTRODUCTION
This application note describes the major difference between Exar’s DUARTs (ST16C2550, XR16L2750,
XR16L2751 and XR16C2850) with TI’s TL16C752B. These devices are very similar, with a few hardware,
firmware-related and bus timing differences.
1.1 HARDWARE DIFFERENCES
• The ST16C2550, XR16L2750, XR16L2751, XR16C2850 and TL16C752B are all available in the 48-pin QFP
package. Additionally, the ST16C2550, XR16L2750 and XR16C2850 are available in the 44-pin PLCC
package and the ST16C2550 and XR16C2850 are available in the 40-pin PDIP package.
• In the QFP package, the ST16C2550, XR16L2750 and TL16C752B are pin-to-pin compatible. The
XR16L2751 and XR16C2850 are not fully pin-to-pin compatible with the TL16C752B. The XR16L2751 has 4
pins that are inputs and the XR16C2850 has 3 pins that are inputs where they are “No Connects” on the
TL16C752B. These extra input pins must be tied to VCC or GND. Please see datasheets for more details.
• Exar’s 48-pin TQFP package is thinner (1.2 mm) than TI’s 48-pin LQFP package (1.6 mm).
• 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,
Exar’s DUARTs will require a 2K pull-up resistor on the XTAL2 pin.
FIGURE 1. CRYSTAL OSCILLATOR CIRCUITRY DIFFERENCES
TL16C752B
Exar DUARTs
XTAL1
C1
10-30 pF
XTAL2
R2
1 ΜΩ
Y1
C2
40-60 pF
R1
1.5 KΩ
1.8432
MHz
to
24
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]