DAN-136 Datasheet, PDF (1/5 Pages) Exar Corporation – EXAR XR16L580 COMPARED

DATA COMMUNICATIONS APPLICATION NOTE
DAN137
November 2003
EXAR XR16L580 COMPARED WITH TI’S TL16C550C (48-TQFP)
Author: BL & PY
1.0 INTRODUCTION
This application note describes the major differences between Exar’s XR16L580 and TI’s TL16C550C (PT and
PFB packages). This application note is applicable to the 48-TQFP package only. These devices are very
similar, with a few minor hardware, bus timing and firmware-related differences. In most applications, the
XR16L580IM will fit and operate in a TL16C550CPT or TL16C550CPFB socket.
1.1 HARDWARE DIFFERENCES (48-TQFP)
• The XR16L580 and TL16C550C are both available in the 48-pin TQFP package. Additionally, the XR16L580
is available in the 32-pin QFN package and the TL16C550C is available in the 44-pin PLCC and 40-pin PDIP
packages. In the 48-pin TQFP package, the XR16L580 and TL16C550C are pin-to-pin compatible, but
some legacy signals are not available (“No Connects”) in the XR16L580 (see Table 1). These legacy signals
are typically not used in most applications, hence they are likely not needed.
• The XR16L580 has two new pins, 16/68# pin to select Intel or Motorola bus and PwrSave pin to reduce I_sleep
(sleep current) to less than 30 uA in Sleep mode. The Power-Save feature is perfect for battery operated
designs. These two pins are ‘No Connects’ in the TL16C550C. Since the 16/68# pin has an internal pull-up
resistor and the PwrSave pin has an internal pull-down resistor in the XR16L580IM, these pins can be left
open when installing the XR16L580 into the TL16C550C socket. The pads on the PCB for these two pins
should have no connection.
• The 32-pin QFN package of the XR16L580 is a new package and should be considered for new designs. It
is the industry’s smallest package full-featured UART well suited for limited board space designs.
• The oscillator circuitry is similar, but there are some differences when using a crystal oscillator and when
using an external clock. See Figure 1 below for the differences in the oscillator circuitry for a crystal oscilla-
tor. For most cases, the XR16L580 will work with the oscillator circuitry for the TL16C550C. When using an
external clock input for frequencies greater than 24 MHz, the XR16L580 will require a 2K pull-up resistor on
the XTAL2 pin. For applications using crystal clock frequencies in the range 1.8432-14.7456MHz, there is vir-
tually no difference in the set up.
1.2 BUS TIMING DIFFERENCES
1.2.1 Chip Select (-CS) and Read (-IOR) / Write (-IOW) Timing
The TL16C550C requires that the -CS pin be asserted first before the -IOR or -IOW pin and the -IOR or -IOW
pin must be de-asserted before the -CS pin is de-asserted. During a read, the Exar UARTs can have either the
-CS or the -IOR signal asserted first and have either signal be de-asserted first. The signals are wire-ORed in
the Exar UARTs, therefore the second signal asserted will initiate the read cycle and the first signal de-
asserted terminates the read cycle. The same is true during a write for -CS and -IOW. The flexibility of the
Exar UARTs timing can be important in DSP, ARM, and MIPS designs. Also, because of this flexibility, the Exar
UARTs will work with the timing used for the TL16C550C.
EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com • [e-mail]