DAN-121 Datasheet, PDF (1/3 Pages) Exar Corporation – EXAR’S XR68C92/192 COMPARED

DATA COMMUNICATIONS APPLICATION NOTE
DAN121
June 2002
EXAR’S XR68C92/192 COMPARED WITH PHILIP’S SCC68692
Author: PY
1.0 INTRODUCTION
This application note describes the major difference between Exar’s XR68C92/192 with Philips’s SCC68692.
These devices are very similar, with a few hardware, firmware-related and bus timing differences.
1.1 HARDWARE DIFFERENCES
• The Philips SCC68692 and Exar XR68C92/192 are both available in two footprints: 44-pin PLCC and 40-pin
PDIP. Additionally, the SCC68692 is available in a 40-pin CDIP and the XR68C92/192 is available in a 44-
pin TQFP. In the PLCC and PDIP packages, the Exar and Philips DUARTs are pin-to-pin compatible.
1.2 FIRMWARE DIFFERENCES
All the internal registers in the SCC68692 and XR68C92/192 are identical with only a few exceptions:
• The XR68C92/192 has an additional mode register, Mode Register 0 (Watch dog timer, RX and TX trigger
levels and extended baud rate tables), for channels A and B while the SCC68692 does not.
• Since the XR88C92/192 has a larger FIFO than the SCC68692, the selectable transmit and receive trigger
levels are different.
• At the address offset of 0x2 and 0xA, the SCC68692 has a read-only BRG Test Register and 1X/16X Test
Register, respectively, while these offsets are reserved for the XR68C92/192.
• The XR68C92/192 has a Miscellaneous Command in the CRA and CRB register bits 7-4 that has a different
function than the SCC68692. When 0xB is written to the upper nibble of CRA or CRB, the XR68C92/192
sets the MR pointer to MR0, but this has no effect on the SCC68692.
1.3 BUS TIMING DIFFERENCES
• The XR68C92/192 is much faster than the SCC68692. For example, the data access time (from -CS low to
data valid) during a read is a maximum of 32 ns for the XR68C92/192, whereas it is a maximum of 175 ns for
the SCC68692.
EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com • [e-mail]