DATA COMMUNICATIONS APPLICATION NOTE DAN160 July 2002 MIGRATING FROM THE XR16C2850 TO THE XR16L2750 Author: PY 1.0 INTRODUCTION This application note describes the changes necessary and what to consider when migrating from the XR16C2850 to the XR16L2750. 1.1 HARDWARE DIFFERENCES • The XR16C2850 and XR16L2750 are both available in the 44-pin PLCC and 48-pin TQFP packages. The XR16C2850 is also available in the 40-pin PDIP package but the XR16L2750 is not. • The XR16C2850 can operate at 3.3 or 5 V only. The XR16L2750 can operate from 2.25 V up to 5.5 V. Also, the XR16L2750 has 5 V tolerant inputs while operating at 3.3 V whereas the XR16C2850 does not. • The maximum crystal oscillator frequency for the XR16C2850 is 8 MHz at 3.3 V while it is a maximum of 20 MHz for the XR16L2750. The crystal oscillator frequency at 5 V and external clock frequencies are the same and the XR16L2750 has the additional specifications for operating at 2.5 V. • In the 44-pin PLCC package, the XR16C2850 and XR16L2750 have identical pinouts so they are fully pin-topin compatible. • In the 48-pin TQFP package, the XR16C2850 has 3 additional pins that are not available in the XR16L2750 but the XR16L2750 can still be a direct drop-in. The following table lists the additional pins of the XR16C2850 and how the same functionality of these pins can be implemented in the XR16L2750. TABLE 1: PIN DIFFERENCES BETWEEN THE XR16C2850 AND XR16L2750 48-TQFP XR16C2850 XR16L2750 PIN PIN NAME PIN NAME NUMBER HARDWARE CHANGES REQUIRED COMMENTS 24 CLK8/16 N.C. None CLK8/16 pin functionality can be selected via EMSR bit-7. 25 CLKSEL N.C. None CLKSEL pin functionality can be selected via MCR bit-7. 37 HDCNTL# N.C. None HDCNTL# pin functionality can be selected via EMSR bit-3. 1.2 FIRMWARE DIFFERENCES The internal registers of the XR16C2850 and XR16L2750 are identical except for a few registers: • FIFO Control Register (FCR) • Bit-0 enables the FIFO for both the XR16C2850 and XR16L2750, but the FIFO sizes are different. The TX and RX FIFOs are 128 bytes deep for the XR16C2850 and are 64 bytes deep for the XR16L2750. • Enhanced Mode Select Register (EMSR) • Bit-7 is not used in the XR16C2850 but it is used in the XR16L2750 to select the 16X or 8X sampling rate. Bit-7 is asserted for 16X sampling (default) and de-asserted for 8X sampling. • Bit-6 is not used in the XR16C2850 but it is used in the XR16L2750 to select whether the LSR Interrupt is generated immediately when there is a data error in the FIFO or delayed until the data byte with an error is being read out of the FIFO. • Bit-3 is not used in the XR16C2850 but it is used in the XR16L2750 to invert the polarity of the RS485 halfduplex direction control output signal (RTS#) if necessary. • Device Identification (DVID) register has a value of 0x12 for the XR16C2850 and 0x0A for the XR16L2750. EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com • [email protected] 1.3 REPLACING THE XR16C2850 WITH THE XR16L2750 You can directly replace the XR16C2850 with the XR16L2750 in the 44-pin PLCC and 48-pin TQFP packages. If using the XR16C2850 in the 40-pin PDIP package, then hardware changes will be required since the XR16L2750 is not available in that package. If using the 8X data sampling rate, BRG prescaler, or RS485 Half-Duplex Control, the software will need to be updated since these functionality control are only implemented in the register bits in the XR16L2750 rather than the hardware pins as available in the XR16C2850. Also, the XR16L2750 has a few additional features such as selecting the LSR interrupt mode and inverting the RS485 polarity that may require some software changes. In a nutshell, the XR16C2850 and XR16L2750 are very similar devices but with different FIFO sizes and there are a few additional features in the XR16L2750. NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. 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 system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 2002 EXAR Corporation August 2002 Send your UART technical inquiry with technical details to hotline: [email protected] Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. 2