DAN-162 Datasheet, PDF (1/2 Pages) Exar Corporation – MIGRATING FROM THE XR16C2852 TO THE XR16L2752

DATA COMMUNICATIONS APPLICATION NOTE
DAN162
August 2002
MIGRATING FROM THE XR16C2852 TO THE XR16L2752
Author: PY
1.0 INTRODUCTION
This application note describes the changes necessary and what to consider when migrating from the
XR16C2852 to the XR16L2752.
1.1 HARDWARE DIFFERENCES
• The XR16C2852 and XR16L2752 are both available in the 44-pin PLCC TQFP package.
• The XR16C2852 can operate at 3.3 or 5 V only. The XR16L2752 can operate at 2.25 V up to 5.5 V. Also,
the XR16L2752 has 5 V tolerant inputs while operating at 3.3 V whereas the XR16C2852 does not have 5 V
tolerant inputs.
• The maximum crystal oscillator frequency for the XR16C2852 is 8 MHz at 3.3 V while it is a maximum of 20
MHz for the XR16L2752. The crystal oscillator frequency at 5 V and external clock frequencies are the
same.
• In the 44-pin PLCC package, the XR16C2852 and XR16L2752 have identical pinouts so they are fully pin-to-
pin compatible.
1.2 FIRMWARE DIFFERENCES
The internal registers of the XR16C2852 and XR16L2752 are identical except for a few registers:
• FIFO Control Register (FCR)
• Bit-0 enables the FIFO for both the XR16C2852 and XR16L2752, but the FIFO sizes are different. The TX
and RX FIFOs are 128 bytes deep for the XR16C2852 and are 64 bytes deep for the XR16L2752.
• Enhanced Mode Select Register (EMSR)
• Bit-7 is not used in the XR16C2852 but it is used in the XR16L2752 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 XR16C2852 but it is used in the XR16L2752 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 XR16C2852 but it is used in the XR16L2752 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 XR16C2852 and 0x0A for the XR16L2752.
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