EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com • uarttechsupport@exar.com

DATA COMMUNICATIONS APPLICATION NOTE

DAN136

June 2002

EXAR’S ST16C452 AND ST16C552 COMPARED WITH TI’S TL16C452

Author: PY

1.0 INTRODUCTION

This application note explains w hy Exar ’s ST16C452 is pin-to-pin compatible with TI’s TL16C452, but Exar ’s

ST16C552 is not pin-to-pin compatible with TI’s TL16C452.

1.1 H

ARDWARE DIFFERENCES

The TI TL16C452 and Exar’s ST16C452 and ST16C552 are all only available in the 68-pin PLCC package.

The TL16C452 has 4 pins that are different from the ST16C452 and ST16C552. Pins 9, 22, 42 and 61 are de-

fined as GND pins on the TL16C452. Those same 4 pins are “No Connections” on the ST16C452. Therefore,

the ST16C4 52 can be a direct drop-i n to the TL16C552. But at those 4 pin lo cations, the ST16 C552 has the

RXRDYA#, TXRDYA#, TXRDYB#, and RXRDYB# outputs respectively. If unused, these outputs should be left

floating and not connected to GND or they will be drawing a lot of current. Therefore, the ST16C552 is not pin-

to-pin co mpatibl e with the TL16C 452 . But it is pin- to-p in co mpatible with the ST1 6C45 2 bec ause the y ar e “No

Connections” at those 4 pins.

1.2 F

IRMWARE DIFFERENCES

1.2.1 Firmware Differences Between the ST16C452 and TL16C452

The ST16C452 is fully software compatible with the TL16C452.

ABLE 1: HARDWARE PIN DIFFERENCES

PIN # TL16C452 ST16C452 ST16C552

9 GND No Connection RXRDYA# Output

22 GND No Connection TXRDYA# Output

42 GND No Connection TXRDYB# Output

61 GND No Connection RXRDYB# Output

NOTICE

EXAR Corporation reserves the right to make changes to the products contained in this publication in order

to improve design, performance or reliability. EXA R Corporation assumes n o responsibility for the use of

any circuits described herein, conveys no license under any patent or other right, and makes no represen-

tation that the circ uits are free of patent infringem ent. C harts and schedul es co ntained here in are only for

illustration purposes and may vary depending upon a user ’s specific applica tion. While the information in

this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies.

EXAR Corporation does not recommend the use of any of its products in life support applications where

the failure or malfunction of the product can reasonably be expected to cause failure of the life support sys-

tem or to significantly affect its safety or effectiveness. Products are not authorized for use in such applica-

tions un les s EX A R Cor po r atio n r ec ei ve s, in writi ng, ass uranc es to its s ati sf ac tion th at: ( a) t he r i sk of inju ry

or damag e has bee n minimi zed; ( b) th e use r assum es al l suc h ri sks; ( c) pote ntial liabi lity of EXA R Cor po-

ration is adequately protected under the circumstances.

Send your UART technical inquiry with technical details

to hotline:

uarttechsupport@exar.com

Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.

1.2.2 Firmware Differences Between the ST16C552 and TL16C452

R = Read-Only, W = Write-Only, R/W = Read/Write

1.3 R

EPLACING THE TL16C452 WITH THE ST16C452 OR ST16C552

You can directly replace TI’s TL16C452 with Exar’s ST16C452 without any hardware or software changes.

When repl acing the TL16C452 with the ST16C5 52, some hardware c hanges will be necessary. Also, the

software should be updated to take advantage of the larger FIFO and enhanced features.

ABLE 2: ST16C552 AND TL16C452 REGISTER SET DIFFERENCES

A2:A0 R/W ST16C552 TL16C452

LCR Bit-7 = 0

001 R/W Interrupt Enable Register (IER)

• Bit-5 = Enable Power Down Mode

Interrupt Enable Register (IER)

• Bit-5 = Not Used

010 R Interrupt Status Register (ISR)

• Bit-7 = FIFO’s Enabled

• Bit-6 = FIFO’s Enabled

Interrupt Status Register (ISR)

• Bit-7 = Not Used

• Bit-6 = Not Used

010 W FIFO Control Register (FCR)

• Enable FIFO, Reset TX/RX FIFO, DMA

Mode, RX Trigger Level s

N/A

100 R/W Modem Control Register (MCR)

• Bit-7 = Power Down

Modem Control Register (MCR)

• Bit-7 = Not Used

101 R Line Status Register (LSR)

• Bit-7 = FIFO Data Error

Modem Control Register (LSR)

• Bit-7 = Not Used