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

• Enhanced Mode Select Register (EMSR)
• Bit-7 is not used in the XR16C2850 but it is used in the XR16L2751 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 XR16L2751 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 XR16L2751 to invert the polarity of the RS485
half-duplex direction control output signal (RTS#) if necessary.
• Device Identification (DVID) register has a value of 0x12 for the XR16C2850 and 0x0A for the
XR16L2751.
1.3 REPLACING THE XR16C2850 WITH THE XR16L2751
You cannot directly replace the XR16C2850 with the XR16L2751 unless pin 12 was connected to VCC or
GND and pin 24 was connected to VCC in the original design.
The PowerSave feature is well suited for low power and batter operated systems. It isolates the data bus
to further reduce current drain during sleep mode. Sleep current can be as low as 30 uA. Please refer to
the XR16L2751 datasheet for complete details.
If using the 8X data sampling rate for the XR16C2850, the software will need to be updated for the
XR16L2751 since this functionality can only be contolled by a register bit rather than as a hardware pin like
that of the XR16C2850. Also, the XR16L2751 has a few additional features such as selecting the LSR in-
terrupt mode and inverting the RS485 polarity that may require some software changes.
In a nutshell, the XR16C2850 and XR16L2751 are very similar devices but with different FIFO sizes and
there are a few additional features in the XR16L2751.
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 represen-
tation 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 sys-
tem or to significantly affect its safety or effectiveness. Products are not authorized for use in such applica-
tions 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 Corpo-
ration is adequately protected under the circumstances.
Copyright 2002 EXAR Corporation
August 2002
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Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
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