DAN-122 Datasheet, PDF (1/3 Pages) Exar Corporation – EXAR’S XR68C681 COMPARED

DATA COMMUNICATIONS APPLICATION NOTE
DAN122
June 2002
EXAR’S XR68C681 COMPARED WITH PHILIP’S SCC68692
Author: PY
1.0 INTRODUCTION
This application note describes the major difference between Exar’s XR68C681 with Philips’s SCC68692.
These devices are very similar, with a few hardware, firmware-related and bus timing differences.
1.1 HARDWARE
• The Philips SCC68692 and Exar XR68C681 are both available in three footprints: 44-pin PLCC, 40-pin
PDIP and 40-pin CDIP. The XR68C681 is pin-to-pin compatible with the SCC68692 in all three footprints.
1.2 FIRMWARE DIFFERENCES
All the internal registers in the SCC68692 and XR68C681 are identical with only a few exceptions:
• 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 XR68C681.
• The XR68C681 has Miscellaneous Commands in the CRA and CRB register bits 7-4 that has different func-
tions than the SCC68692. See the table below.
TABLE 1: MISCELLANEOUS COMMAND DIFFERENCES IN COMMAND REGISTER A/B
CR A/B
BIT-7
1
1
1
1
1
1
1
CR A/B
BIT-6
0
0
0
0
1
1
1
CR A/B
BIT-5
0
0
1
1
0
0
1
CR A/B
BIT-4
0
1
0
1
0
1
0
XR68C681
Set RX BRG Select Extend Bit
Clear RX BRG Select Extend Bit
Set TX BRG Select Extend Bit
Clear TX BRG Select Extend Bit
Channel A: Set Standby (Low
Power) Mode
Channel A: Set Active (Normal
Power) Mode
Reserved
1
1
1
1
Reserved
SCC68692
Assert RTSN
Negate RTSN
Set Timeout Mode On
Not Used
Disable Timeout Mode
Not Used
Set Standby (Low Power) Mode
(CRA Only)
Set Active (Normal Power Mode
(CRA Only)
EXAR Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com • [e-mail]