DAN-161 Datasheet, PDF (1/2 Pages) Exar Corporation – MIGRATING FROM THE XR16C2850 TO THE XR16L2751

DATA COMMUNICATIONS APPLICATION NOTE
DAN161
August 2002
MIGRATING FROM THE XR16C2850 TO THE XR16L2751
Author: PY
1.0 INTRODUCTION
This application note describes the changes necessary and what to consider when migrating from the
XR16C2850 to the XR16L2751.
1.1 HARDWARE DIFFERENCES
• The XR16C2850 and XR16L2751 are both available in the 48-pin TQFP package. The XR16C2850 is also
available in the 40-pin PDIP and 44-pin PLCC packages but the XR16L2751 is not.
• The XR16C2850 can operate at 3.3 or 5 V only. The XR16L2751 can operate from 2.25 V up to 5.5 V. Also,
the XR16L2751 is 5 V tolerant while operating at 3.3 V.
• 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 XR16L2751. The crystal oscillator frequency at 5 V and external clock frequencies are the same
and the XR16L2751 has the additional specifications for operating at 2.5 V.
• IER Bit-4 enables the sleep mode for both the XR16C2850 and XR16L2751. But if the PWRSAVE pin (pin
12) of the XR16L2751 is tied to VCC, then the XR16L2751 will be in PowerSave Mode where, in addition to
sleep mode, the data bus interface is isolated further reducing power consumption. Please see datasheet for
complete details. This pin is not available in the XR16C2850.
• The XR16C2850 can only operate in the Intel Bus Interface. But the XR16L2751 can operate in either the
Intel or Motorola Bus Interface. If the 16/68# pin (pin 24) is tied to VCC, the XR16L2751 is in the Intel Bus
Interface and if the 16/68# pin is tied to GND, the XR16L2751 will be operating in the Motola Bus Interface.
• In the 48-pin TQFP package, there are 2 pins that are different between the XR16C2850 and the
XR16L2751. The following table lists the pin differences and the hardware changes necessary to replace the
XR16C2850 with the XR16L2751.
TABLE 1: PIN DIFFERENCES BETWEEN THE XR16C2850 AND XR16L2751
48-TQFP
PIN
NUMBER
XR16C2850
PIN NAME
XR16L2751
PIN NAME
12
N.C. PWRSAVE
24
CLK8/16 16/68#
HARDWARE
CHANGE
REQUIRED
Yes
Yes
COMMENTS
PWRSAVE pin on the XR16L2751 is an input and therefore should
be connected GND or VCC
Needs to be connected to VCC to select the Intel Bus Interface.
CLK8/16 pin functionality can be selected via EMSR bit-7.
1.2 FIRMWARE DIFFERENCES
The internal registers of the XR16C2850 and XR16L2751 are identical except for a few registers:
• FIFO Control Register (FCR)
• Bit-0 enables the FIFO for both the XR16C2850 and XR16L2751, 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 XR16L2751.
EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com • [e-mail]